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READINGS  IN  EVOLUTION, 
GENETICS,  AND  EUGENICS 


THE  UNIVERSITY  OP  CHICAGO  PRESS 
CHICAGO.  ILLINOIS 


THE  BAKER  &  TAYLOR  COMPANY 

NEW  YORK 


THE  CAMBRIDGE  UNIVERSITY  PRESS 

LONDON 

THE  MARUZEN-KABUSHIKI-KAISHA 

TOKYO,  OSAKA,  KYOTO,  FUKUOKA,  SENDAI 

THE  MISSION  BOOK  COMPANY 

SHANGHAI 


READINGS  IN  EVOLUTION, 
GENETICS,  AND  EUGENICS 


By 

HORATIO  HACKETT  NEWMAN 

Professor  of  Zoology  in  the 
University  of  Chicago 


^O'^rOV'- 


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THE  UNIVERSITY  OF  CHICAGO  PRESS 
CHICAGO,  ILLINOIS 


Copyright  192  i  By 
The  University  of  Chicago 


All  Rights  Reserved 


Published  October  192 1 


Composed  and  Printed  By 

The  University  of  Chicago  Press 

Chicago,  Illinois,  U.S.A. 


THIS  VOLUME 

IS  AFFECTIONATELY   DEDICATED 

TO 

MY  MOTHER 


3265S 


PREFACE 

This  book  has  been  prepared  to  meet  a  specific  demand,  long 
felt  here  and  elsewhere,  for  an  account  of  the  various  phases  of  evolu- 
tionary biology  condensed  within  the  scope  of  one  volume  of  moderate 
size.  The  present  writer  has  now  for  sixteen  successive  years  pre- 
sented in  lecture  form  to  large  classes  of  students  the  subjects  of 
evolution,  genetics,  and  eugenics.  Never  have  we  been  able  to  find 
a  single  book  that  would  cover  the  required  ground.  In  fact  it  has 
been  necessary  to  require,  or  at  least  to  recommend,  as  many  as 
three  books.  It  is  believed  that  the  present  book  will  furnish  ade- 
quate reading  material  for  a  major  or  a  semester  course  in  evolutionary 
biology.  Some  supplementary  reading  may  be  necessary  in  case  an 
instructor  wishes  to  emphasize  one  or  more  phases  of  the  subject; 
but  for  a  first  course  in  the  subject  we  believe  that  all  of  the  essential 
reading  material  will  be  found  within  the  text  itself. 

An  effort  has  been  made  to  present  the  subject  in  the  best  peda- 
gogical order.  After  a  general  introduction,  a  rather  long  chapter 
appears  in  which  the  whole  history  of  the  development  of  evolution- 
ary science  is  outlined,  together  with  the  names  and  contributions 
of  the  leading  evolutionists.  Part  II  is  a  presentation  of  the  evi- 
dences of  organic  evolution,  beginning  with  the  bodies  of  evidence 
most  definite  and  direct,  and  ending  with  the  less  definite  and 
more  controversial.  Part  III  deals  with  causo-mechanical  theories  of 
evolution  with  Darwinism  as  the  central  topic.  Part  I\'  concerns 
itself  with  genetics  or  modern  experimental  evolution,  and  Part  V 
with  eugenics,  or  genetics  as  applied  to  human  improvement. 

The  book  consists  largely  of  excerpts,  some  long  and  some  short, 
from  both  the  older  classical  evolutionary  writers  and  the  modern 
writers.  Our  aim  has  been  to  select  the  most  significant  or  character- 
istic passages  from  each  author.  In  most  cases  this  ideal  has  been 
attained,  but  it  has  sometimes  happened  that  we  have  had  to  make 
our  selection  of  material  to  meet  a  real  need  in  the  book,  and  accord- 
ingly have  selected  from  an  author  a  passage  he  himself  might  not 
consider  particularly  characteristic  of  his  work.  We  have  succeeded, 
nevertheless,  in  welding  together  out  of  a  collection  of  isolated  chai^ers 
and  passages  what  seems  to  us  to  be  a  close  approach  to  a  coherent 
unit.  Unification  has  been  accomplished  by  the  aid  of  editorial 
connecting  passages,  introductory  statements,  criticisms,  and  sum- 
maries.    In  certain  cases  it  became  necessar}^,  for  a  variety  of  reasons, 

•  • 
Vll 


viii  PREFACE 

for  the  editor  to  write  short  chapters  on  certain  topics  that  were  not 
presented  in  the  available  literature  in  sufficiently  brief  compass  or 
in  sufficiently  non-technical  language. 

The  one-man  textbook  is  only  too  often  written  to  emphasize 
the  author's  pet  theories  and  is  likely  to  be  unduly  biased.  The 
present  work  is  completely  non-partisan.  It  consists  of  the  writ- 
ings of  many  authors  and  presents  many  diverse  theories.  The 
student  is  left  to  balance  the  various  views  one  against  another  and 
to  form  his  own  judgment. 

It  is  very  unfortunate,  but  none  the  less  true,  that  even  in  these 
scientific  days,  the  subject  of  evolution  has  a  bad  name  in  many 
communities,  and  in  many  educational  institutions  with  religious 
affiliations.  The  mistake  is  made  of  supposing  that  evolution  and 
religion  are  diametrically  opposed.  The  present  writer  has  been  at 
some  pains  to  make  it  clear  that  evolution  and  religion  are  strictly 
compatible.  We  teachers  of  evolution  in  the  colleges  have  no  sinister 
designs  upon  the  religious  faith  of  our  students. 

While  this  book  is  intended  primarily  for  a  college  textbook, 
we  have  also  had  in  mind  the  general  reader.  Apart  from  a  few  of 
the  more  technical  details,  the  text  seems  to  us  very  readable.  The 
language  of  the  great  classic  writers — Darwin,  Wallace,  Romanes,  De 
Vries,  Le  Conte — is  simple  and  lucid.  Among  recent  biological  books 
few  are  written  so  freshly  and  vividly  as  those  of  Professor  J.  Arthur 
Thomson.  The  clearness  and  scientific  accuracy  of  Conklin,  Saleeby, 
Guyer,  Walter,  Lull,  Osborn,  the  Coulters,  Downing,  Shull,  Tayler, 
Popenoe,  Johnson,  and  others,  are  familiar  to  American  biologists. 

Scrupulous  care  has  been  taken  to  verify  all  passages  quoted, 
but  it  is  hardly  likely  that,  in  so  large  a  mass  of  material,  all  errors 
shall  have  been  avoided.  The  author  and  the  publishers  would 
welcome  as  a  favor  any  suggestions  or  corrections  submitted  by 
interested  readers. 

A  list  of  fifty  books  from  which  material  has  been  quoted  is  given 
on  pages  510-512.  To  the  authors  and  publishers  of  these  books  and 
monographs  we  wish  herewith  to  tender  our  grateful  acknowledg- 
ments for  their  generosity  and  co-operation.  A  considerable  amount 
of  material  for  which  permission  to  reprint  had  been  granted  fails 
to  appear  in  the  present  volume.  It  is  hoped  to  incorporate  this 
material  in  an  appendix  to  a  later  edition,  or  else  to  use  it  in  the  form 
of  a  small  volume  of  supplementary  readings. 

H.  H.  N. 
August  15,  1921 


TABLE  OF  CONTENTS 


PAGE 


List  of  Illustrations xv-xviii 

PART  I.     INTRODUCTORY  AND  HISTORICAL 

Chapter  I.    Introduction 3 

"vlVhat  Organic  Evolution  Is — Definitions 3 

^yrhe  Modern  Attitude  as  to  the  Truth  of  the  Evolution  Doctrine  .  5 

'VWhat  Organic  Evolution  Is  Not 8 

Chapter  II.    Historical  Account  of  the  Development  of  the 

Evolution  Theory.    H.H.N 10 

Evolution  among  the  Greeks 11 

Post-x\ristotelians 14 

The  Early  Theologians 14 

The  Revival  of  Science 15 

The  Great  Naturalists  of  the  Eighteenth  Century 16 

X  Lamarck 18 

Cuvier  and  Geofifroy  St.  Hilaire 21 

Catastrophism  and  Uniformitarianism 22 

The  Reawakening  of  the  Evolution  Idea 23 

Charles  Darwin 24 

">■■  Summary  of  Darwin's  Theories 25 

Contemporary  Opinion  Regarding  the  Validity  of  Darwin's  Views  27 

Isolation  Theories ^^ 

Orthogenesis  Theories H 

Mutation  or  Heterogenesis  Theories 36 

The  Rise  and  Vogue  of  Biometry 3^ 

\^Modern  Experimental  Evolution 39 

^V^Iendel's  Laws -^^ 

Hybridization  and  the  Origin  of  Species 43 

Neo-Mendelian  Developments 43 

heredity  and  Sex 44 

Chapter  III.    The    Relation   of   Evolution   to   Materialism. 

Joseph  Le  Conte 4o 

PART  II.     EVIDENCES  OF  ORGANIC  EVOLUTION 
Chapter  IV.    Is  Organic  Evolution  an  Established  Principle  ? 

H.H.N "^^ 

Chapter  V.    Evidences  from  Palaeontology 61 

Strength  and  Weakness  of  the  Evidence ^^ 

ix 


>v 


X  TABLE  OF  CONTENTS 

_  PAGE 

\pther  Opinions  as  to  the  Adequacy  of  the  Evidences  from  Palae- 
ontology   62 

What  Fossils  Are  and  How  They  Have  Been  Preserved  ....  63 

Fossils  Classified 63 

On  the  Conditions  Necessary  for  Fossilization 64 

On  the  Lapse  of  Time  during  Which  Evolution  Is  Believed  to  Have 

Taken  Place 67 

On  the  Principal  General  Facts  Revealed  by  a  Study  of  the  Fossils  69 

Fossil  Pedigrees  of  Some  Well-known  Vertebrates 70 

Pedigree  of  the  Horse         70 

Pedigree  of  the  Camels.     W.  B.  Scott 73 

Evolution  of  the  Elephants.     A.  Franklin  Shull 76 

Chapter  VI.    The  Evolution  of  Man:  Palaeontology.    Richard 

Swann  Lull 81 

Origin  of  Primates 81 

Origin  of  Man 82 

Fossil  Man 84 

Evidences  of  Human  Antiquity 94 

Future  of  Humanity 95 

Chapter  VII.    Evidences  from  Geographic  Distribution      ,     .  97 
Some  of  the  More  Significant  Facts  about  the  Distribution  of 

Animals loi 

The  Fauna  of  Oceanic  Islands.     George  John  Romanes      .      .      .  loi 

The  Fauna  of  Madagascar  and  New  Zealand.     A.  R.  Wallace    .  no 

The  Distribution  of  Marsupials.     A.  R.Wallace in 

The  Distribution  of  Birds.     A.  R.Wallace *.  112 

Summary  of  Mammalian  Dispersal.     Hans  Gadow      .      .      .      .  114 
Summary  of  the  Argument  for  Evolution  as  Based  on  Geographic 

Distribution 115 

Chapter  VIII.    Evidences  from  Classification 117 

The  Principles  of  Classification.     A.  F.  Shull 117 

The  Method  of  Classification.     Charles  Darwin 120 

What  Is  a  Species  ? 121 

Chapter  IX.    Evidence  from  Blood  Tests.    W.B.Scott  .     .     .  124 

Chapter  X.    Evidences  from  Morphology  (Comparative  Anat- 
omy).    George  John  Romanes 129 

Chapter  XL    Evidences  from  Embryology 164 

The  Facts  of  Reproduction  and  Development 164 

Outline  of  Animal  Development.     D.  S.  Jordan  and  V.  L.  Kellogg  .  165 

Chapter  XII.    Critique  of  the  Recapitulation  Theory.     W.  B. 

Scott 173 


TABLE  OF  CONTENTS  xi 

PART  III.     THE  CAUSAL  FACTORS  OF  ORGANIC  EVOLUTION 


PAGE 


Chapter  XIIL    Introductory  Statement 185 

What  We  Owe  to  Darwin 186 

Chapter  XIV.    The  Background  of  Darwinism-— 

Adaptations.    H.H.N 188 

Laws  of  Adaptation 192 

Adaptations  Classified 195 

Some  Special  Adaptations 196 

Parasitism  and  Degeneration 197 

Color  in  Animals 200 

Chapter  XV.    The  Background  of  Darwinism — Continued     .     .  206 

The  Web  of  Life.     /.  Arthur  Thomson 206 

Chapter  XVI.    Natural  Selection.    Charles  Darwin    .     .     .     .  219 

Foundation  Stones  of  Natural  Selection 219 

Darwin's  Own  Estimate  as  to  the  Role  of  Natural  Selection  in 

Evolution 219 

Effects  of  Habits  and  the  Use  or  Disuse  of  Parts;    Correlated 

Variation;  Inheritance 220 

Darwin's  Idea  of  the  Causes  Responsible  for  the  Origin  of  Domes- 
tic Races 221 

Darwin's  Idea  of  the  Origin  of  Varieties,  Species,  and  Genera  in 

Nature 221 

The  Term  "Struggle  for  Existence"  Used  in  a  Large  Sense  .     .  222 

Geometrical  Ratio  of  Increase ■  ^^S 

Natural  Selection ;  Or  the  Survival  of  the  Fittest 223 

Sexual  Selection 230 

Illustrations  of  the  Action  of  Natural  Selection,  or  the  Survival 

of  the  Fittest 232 

Summary  of  Chapter  on  Natural  Selection 233 

Difficulties  and  Objections  to  Natural  Selection  as  Seen  by  Darwin  236 

Chapter  XVH.     Critique  of  Darwinism 245 

Summary    of    Darwin's    Natural-Selection    Theory.     Vernon    L. 

Kellogg 2-^5 

Objections  to  Darwinism 247 

Defense  of  Darwinism ^52 

General  Defense  of  Darwinism.     /.  L.  Tayler 253 

Experimental  Support  of  the  Effectiveness  of  Natural  Selection     .  256 

The  Present  Status  of  Natural  Selection 2 58 

The  Relation  of  Mendelism  and  the  Mutation  Theory  to  Natural 

Selection.     C.  C.  Nutting 258 


xii  TABLE  OF  CONTENTS 

PAGE 

Chapter  XVIII.    Other  Theories  of  Species-Forming      ...  263 

Theories  Auxiliary  to  Natural  Selection 263 

Weismann's  Theory  of  Panmixia 263 

Weismann's  Theory  of  Germinal  Selection 265 

Roux's  Theory  of  Intraselection  or  the  Battle  of  the  Parts    .      .  268 

Coincident  Selection  or  Organic  Selection 268 

Isolation  Theories 269 

Theories  Alternative  to  Natural  Selection 273 

Chapter  XIX.    A  New  Composite  Causo-Mechanical  Theory 
OF  Evolution  (the  Tetr akinetic  Theory),    Henry  Fairfield 

Oshorn 275 

The  Energy  Concept  of  Life 275 

The  Four  Complexes  of  Energy 280 

PART  IV.     GENETICS 

Chapter  XX.    The  Scope  and  Methods  of  Genetics   .     .     .     .  287 

Definitions 287 

The  Scope  and  Methods  of  Genetics 287 

The  Importance  of  the  Cell  Theory  in  Genetics 289 

Chapter  XXL     The  Bearers  of  the  Heritage  (an  Account  of  the 

Cellular  Basis  of  Heredity).     Michael  F.  Guy er 290 

Chapter    XXII.     Variation.     Ernest    Brown    Babcock    and    Roy 

Elwood  Clausen 307 

Chapter  XXIII.    Are    Acquired    Characters    (Modifications) 

Hereditary? 323 

Misunderstandings  as  to  the  Question  at  Issue.  /.  Arthur  Thom- 
son       323 

The    Inheritance    or    Non-Inheritance    of    Acquired    Characters. 

Edwin  Grant  Conklin 330 

The  Other  Side  to  the  Question- 336 

A  Possible  Mechanism  for  the  Transmission  of  Acquired  Characters. 

Michael  F.  Giiyer 338 

Chapter  XXIV.    The  Mutation  Theory 346 

New  Species  (Mutants)  of  Oenothera.     Hugo  De  Vries     ....  348 

Summary  of  De  Vries's  Mutation  Theory.     Thomas  Hunt  Morgan  .  355 

Criticisms 359 

Causes  of  Mutations 360 

Chapter  XXV.    Biometry  (the  Statistical  Study  of  Variation 

and  Heredity).    H.H.N 365 

The  Statistical  Study  of  Variation 365 

Bimodal  and  Multimodal  Curves 368 

The  Coefficient  of  Correlation 369 

Statistical  Study  of  Inheritance.     Edwin  Grant  Conklin     .      .      .  370 


TABLE  OF  CONTENTS  xiii 


PAGE 


Chapter  XXVI.    Heredity  in  Pure  Lines.    H.H.N 376 

Are  Determiners  (Genes)  Constant  or  Variable  ? 378 

Chapter  XXVII.      Mendel's  Laws  of  Heredity 380 

Mendel's  Life  and  Character.    /.  Arthur  Thomson 380 

Mendel's  Discoveries.     /.  Arthur  Thomson 380 

Mendel's  Explanations.     /.  M.  Coulter  and  M.  C.  Coulter    .     .      .  386 
Illustrations  of  Simple  Mendelian  Inheritance  in  Both  Animals  and 

Plants.     J.  Arthur  Thomson 393 

Chapter  XXVIII.    The  Physical  Basis  of  Mendelism.    Ernest 

B.  Bahcock  and  Roy  E.  Clausen 401 

Chapter  XXIX.    Neo-Mendelism  in  Plants.    John  M.  Coulter 

and  Merle  C.  Coulter 413 

Presence  and  Absence  Hypothesis 413 

Blends 415 

The  Factor  Hypothesis 417 

Chapter  XXX.    Neo-Mendelian  Heredity  in  Animals.  H.H.N.  429 

Illustrations  of  the  Factor  Hypothesis ,     .  429 

The  Factorial  Analysis  of  Color  in  Mice 429 

Different  Kinds  of  Albinos 430 

Castle's  Guinea  Pigs 43 1 

Chapter  XXXL    Sex-linked    and    Other    Kinds    of    Linked 
Inheritance  in  Drosophila  and  Other  Species.    William  E. 

Castle 433 

Drosophila  Type  and  Poultry  Type  of  Sex-linked  Inheritance     .      .  436 

Chapter  XXXII.    Linkage    and    Crossing-Over.    William    E. 

Castle 441 

Chapter  XXXIII.    Sex  Determination.    H.H.N 449 

Various  Theories  of  Sex  Determination 449 

The  Chromosomal  Mechanism  of  Sex  Determination      ....  450 

Sex  Determination  in  Parthenogenetic  Species 451 

The  Poultry  Type  of  Sex  Determination 45^ 

Sex  Differentiation 453 

PART  V.    EUGENICS 

Chapter  XXXIV.    The    Inheritance    of    Human    Characters, 

Physical  and  Mental.    Elliot  R.  Downing 459 

Chapter  XXXV.    Human  Conservation.    Herbert  E.  Walter  .     .473 

How  Mankind  May  Be  Improved 473 

More  Facts  Needed • -^'-^ 

Further  Application  of  What  We  Know  Necessary 474 

The  Restriction  of  Undesirable  Germplasm 475 

Control  of  Immigration 475 


xiv  TABLE  OF  CONTENTS 

PAGE 

More  Discriminating  Marriage  Laws 477 

An  Educated  Sentiment 477 

Segregation  of  Defectives 478 

Drastic  Measures 479 

The  Conservation  of  Desirable  Germplasm 480 

By  Subsidizing  the  Fit 480 

By  Enlarging  Individual  Opportunity 481 

By  Preventing  Germinal  Waste 481 

Who  Shall  Sit  in  Judgment  ? 482 

Chapter  XXXVI.    Eugenics  and  Euthenics.    Paul  Popenoe  and 

Roswell  H.  Johnson 484 

Chapter  XXXVII.    The    Promise    of    Race    Culture.    Caleb 

Williams  Saleeby 497 

Bibliography 510 

Index 515 


LIST  OF  ILLUSTRATIONS 


PAGE 


1.  Total  Geologic  Time  Scale 68 

2.  Feet  AND  Teeth  IN  Fossil  Pedigree  OF  THE  Horse     ...  72 

3.  Four  Stages  IN  THE  Evolution  OF  THE  Cameline  Skull     .     .  74 

4.  Four  Stages  in  the  Evolution  of  the  Cameline  Fore  Foot   ,  7  5 

5.  Evolution  of  Head  and  Molar  Teeth  of  Mastodons  and 

Elephants 77 

6.  Skull  of  Java  Ape-Man,  Pithecanthropus  erectus      ....  87 

7.  Jaws  of  Man  and  of  the  Apes 88 

8.  Restoration  of  Prehistoric  Men 90 

9.  Neanderthaloid  Skull  of  La  Chapelle-aux-Saints  ...  91 

10.  Skeleton  of  Neanderthal  Man 92 

11.  Skeleton  OF  Seal 130 

12.  Skeleton  OF  Greenland  Whale 132 

13.  Paddle  of  Whale  Compared  with  Hand  of  Man  .     .     .     .  133 

14.  Wing  of  Reptile,  Mammal,  and  Bird 134 

15.  ^KE'LETO^  O'F  Dinornis  gravis 137 

16.  Hermit  Crabs  Compared  with  Cocoa-nut  Crab     ....  139 

17.  Rudimentary  or  Vestigial  Hind  Limbs  of  Python     .     .     .  141 

18.  Apteryx  australis 142 

19.  Illustrations  of  the  Nictitating  Membrane  in  the  \' arious 

Animals ^47 

20.  Rudimentary,  or  Vestigial  and  Useless,  Muscles  of  the 

Human  Ear 148 

21.  Portrait  OF  a  Young  Gorilla i4Q 

22.  Lower  Extremities  OF  a  Young  Child 150 

23.  An  Infant,  Three  Weeks  Old,  Supporting  Its  Own  Weight 

FOR  Over  Two  Minutes 151 

24.  Sacrum  OF  Gorilla  Compared  with  That  OF  Man      .     .     .  152 

25.  Diagrammatic  Outline  of  the  Human  Embryo  When  about 

Seven  Weeks  Old ^S3 

26.  Front  AND  Back  View  OF  Adult  Human  Sacrum    .     .     .     .  i53 

27.  Appendix  vermiformis  ii<i  Oratsig  AiiD  IN  Mai<s i54 

28.  Appendix  vermiformis  in  Orang  and  Man,  Showing  Variation 

in  the  Orang -^54 

XV 


xvi  LIST  OF  ILLUSTRATIONS 

PAGE 

29.  Human  Ear  Modeled  and  Drawn  by  Mr.  Woolner  .     .      .  155 

30.  Foetus  of  an  Orang 156 

31.  Vestigial  Characters  or  Human  Ears 157 

T^2.  Hair  Tracts  ON  THE  Arms  AND  Hands  OF  Man 159 

2)T).  Molar  Teeth  of  Lower  Jaw  in  Gorilla,  Orang,  and  Man  .  161 

34.  Perforations  of  the  Humerus  in  Three  Species  of  Quad- 

rumana 162 

35.  First  Stages  in  the  Embryonic  Development  of  the  Pond 

Snail,  Lymnaeus 166 

36.  Stages  IN  THE  Development  OT  THE  Vrawn,  Peneus  potimirium  170 

37.  Later  Stages  in  the  Development  of  the  Prawn,  Peneus 

potimirium 170 

38.  Metamorphosis  OF  A  Barnacle,  Ze^aj 171 

39.  Embryos   in    Corresponding    Stage    of    Development    of 

Shark,  Fowl,  and  Man 177 

40.  Three  Aquatic  Types  of  Vertebrate,  to  Illustrate  Con- 

vergent Adaptation 193 

41.  Fierasfer  acus,  penetrating  the  Anal  Openings  of  Holo- 

THURIANS 199 

42.  Kallima,  the  "Dead-Leaf  Butterfly" 202 

43.  Diagram  of  a  Cell,  Showing  Various  Parts 291 

44.  Diagram  Showing  Representative  Stages  in  Mitotic  or 

Indirect  Cell-Division 292 

45.  Germ  Cell  Set  Apart  in  the  Eight-Celled  Stage  of  Cleav- 

age IN  M  last  or  americana 295 

46.  Chromosomes  of  the  Mosquito  and  of  the  Fruit  Fly     .     .  297 

47.  Diagram  to  Illustrate  Spermatogenesis 298 

48.  Diagram  to  Illustrate  Oogenesis 299 

49.  Diagram  Showing  the  Parallel  between  Maturation  of 

THE  Sperm  Cell  and  Maturation  of  the  Ovum  ....  300 

50.  Diagram  to  Illustrate  Fertilization 302 

51.  Variation  in  Sedum  spectahile  Due  to  Differences  in  Colo?l 

of  Light 313 

52.  Temperature  Phases  of  the  Diurnal  Peacock-Butterfly  .  314 

53.  Morphological  Cycle  OF  Head  Height  IN  fl'>'a/o(/a/>/fma.     .  315 

54.  Schematic   Curves   of   Head   Height   in  Hyalodaphnia  as 

Grown  IN  Media  OF  Three  Different  Food  Values    .     .  316 

55.  Climatic  Effects  UPON  Plumage  IN  Pigeons 317 

56.  Effects  of  Injections  into  Ovary  of  Scrophularia.     .     .     .  319 


LIST  OF  ILLUSTJL\TIONS  xvii 


PAGE 


57.  Oenothera  lamarckiana 347 

58.  A  Series  Showing  Oenothera  lamarckiana  and  Several  of  Its 

Mutants  Growing  Side  by  Side 352 

59.  Diagram  Showing  in  Condensed  Form  the  Genealogy  of 

THE  Oenothera  lamarckiana  Family  and  Its  Various  Mutants    357 

60.  Some  Divergent  Types  (Mutations)  of  Beetles  Produced 

BY  Subjecting  the  Germ  Cells  to  External  Influences    361 

61.  Two  Plants   of  Onagra  biennis,   Showing  the   Effect  of 

Injections  of  Zinc  Sulphate  into  the  Ovule     ....     362 

62.  Polygon  of  Variation  for  the  Total  Number  of  Scutes  in 

THE  Nine  Bands  of  the  Armadillo 366 

63.  BiMODAL  Polygon  Plotted  from  Data  on  the  Earwig     .     .  369 

64.  Correlation  Table  of  400  Plants  of  Sixty-Day  Oats    .  370 

65.  Diagram  of  Galton's  "Law  of  Ancestral  Inheritance"     .  372 

66.  Scheme  to  Illustrate  Galton's  "Law  of  Filial  Regression  "  374 

67.  Diagram    Illustrating    Behavior    of    Chromosomes    in 

Mendel's  Cross  of  Tall  and  Dwarf  Peas 388 

68.  Diagram  Illustrating  Behavior  of  First  Hybrid  Genera- 

tion When  Inbred 389 

69.  Diagram  Illustrating  Dihybrid  Ratio 392 

70.  Diagram  Showing  the  Characteristic  Pairing,  Size  Rela- 

tions,  and   Shapes   of   the   Chromosomes  of  Drosophila 
ampelophila 402 

71.  Diagram  of  Mitosis  in  a  Species  Having  Four  Chromo- 

somes in  Its  Cells 4^4 

72.  The  Reduction  Division  as  Represented  for  a  Species 

Whose  Diploid  Number  Is  Four 406 

73.  Diagram   of    Chromatin   Interchange   bet\\ten   Homolo- 

gous Members  of  a  Pair  of  Chromosomes 408 

74.  Diagram  Showing  Consequences  of  Independent  Segrega- 

tion OF  Chromosomes  in  Drosophila  ampelophila  ....     409 

75.  Diagram  to  Show  Chromosome  Relations  in  the  Inherit- 

ance OF  Sex  in  Drosophila  ampelophila 4 1 1 

76.  Diagram  Showing  How  the   Original  Scheme   Must  Be 

Modified  to  Satisfy  the  Presence  and  Absence  Hypothe- 
sis       ^'^ 

77.  Diagram  Showing  How  Presence  and  Absence  Scheme  Is 

Actually  Used *^^^ 

78.  Diagram  Illustrating  Blending  Inheritance 416 


xviii  LIST  OF  ILLUSTRATIONS 

PAGE 

79.  Diagram  Illustrating  Complementary  Factors   .     .     .     .     418 

80.  Diagram  Illustrating  Behavior  OF  iNinBiTORY  Factor  .     .     421 

81.  Diagram  Sho\\tng  Some  Possible  Combinations  in  Fa  When 

Fi  OF  Figure  80  Is  Inbred 422 

82.  Diagram  Showing  the  Heterozygote  Situation    .     .     .     .     422 

83.  Diagram  Illustrating  the  Action   of  a   Supplementary 

Factor 423 

84.  Diagram  Illustrating  Nilsson-Ehle's  Explanation  of  the 

15:1  Ratio  in  F2  of  Hybrid  between  Red-  and  White- 
grained  Wheat 425 

85.  Another  Method  of  Visualizing  Nilsson-Ehle's  15:1  Ratio    426 

86.  Diagram  of  Nilsson-Ehle's  6s  :  i  Ratio  .     .     .     .     .     .     .     427 

87.  Sex-Linked  Inheritance  of  White  and  Red  Eyes  in  Droso- 

phila 434 

88.  Reciprocal  Cross  to  That  Shown  in  Figure  87     .     .     .     .435 

89.  Drawing  Showing  the  Four  Pairs  of  Chromosomes  Seen  in 

THE  Dividing  Egg  of  Drosophila 436 

90.  Diagram  Showing  the  Location  in  the  Four  Paired  Chromo- 

somes OF  Drosophila,  of  the  Genes  for  Various  Mendeliz- 
ING  Characters,  as  Determined  by  Morgan 437 

91.  Sex-Linked  Inheritance  of  Barred  and  Unbarred  (Black) 

Plumage  in  Poultry 438 

92.  Reciprocal  Cross  to  That  Shown  in  Figure  91     ...     .     439 

93.  Diagram  to  Show  the  Mechanism  of  Crossing  Over  .     .     .     440 

94.  An  Armadillo  Egg  about  Six  Weeks  after  Fertilization, 

Showing  the  Quadruplet  Foetuses 451 

95.  A  Typical  Opposite-Sexed  Pair  of  Cattle  Twins  ....     455 

96.  A  Pedigree  of  Brachydactylism 460 

97.  A  Pedigree  Showing  Transaussion  of  Cataract   .     .     .     .461 

98.  A  Pedigree  Showing  Heredity  of  Feeble-Mindedness  .     .     463 

99.  Another  Pedigree  Showing  Heredity  of  Feeble-Minded- 

ness   464 

100.  Pedigree  Showing  Heredity  of  Insanity 465 

loi.  Pedigree  Showing  Heredity  of  Insanity  and  Neurotic 

Tendency 465 


PART  I 
INTRODUCTORY  AND  HISTORICAL 


CHAPTER  I 
INTRODUCTION 

WHAT   ORGANIC   EVOLUTION  IS — DEFINITIONS 

[The  following  selections  are  representative  both  of  the  older  and 
of  the  newer  attitudes  of  thinkers  on  the  subject  of  organic  evolution. 
The  earlier  writers  were  greatly  impressed  with  the  sublimity  of  the 
idea  and  found  it  in  full  accord  with  their  religious  faith.  The  later 
writers  are  less  awed  by  the  vastness  of  the  process  and  hence  adopt 
a  more  completely  materialistic  attitude.  It  is  not  necessary,  how- 
ever, to  discard  one's  religious  beliefs  in  order  to  adopt  a  scientific 
attitude  toward  the  problems  of  organic  evolution.^  These  points  of 
view  are  well  expressed  in  the  following  quotations. — Ed.] 

''The  world  has  been  evolved,  not  created;  it  has  arisen  little  by 
little  from  a  sm.all  beginning,  and  has  increased  through  the  activity 
of  the  elemental  forces  embodied  in  itself,  and  so  has  rather  grown  than 
suddenly  come  into  being  at  an  almighty  word.  What  a  sublime  idea 
of  the  infinite  might  of  the  great  Architect!  the  Cause  of  all  causes, 
the  Father  of  all  fathers,  the  Ens  entium!  For  if  we  could  compare 
the  Infinite  it  would  surely  require  a  greater  Infinite  to  cause  the 
causes  of  effects  than  to  produce  the  effects  themselves. 

"All  that  happens  in  the  world  depends  on  the  forces  that  prevail 
in  it,  and  results  according  to  law;  but  where  these  forces  and  their 
substratum.  Matter,  come  from,  we  know  not,  and  here  we  have  room 
for  faith.  "—Erasmus  Darwin,^  as  interpreted  by  Weismann. 

"When  I  first  came  to  the  notion,  ....  of  a  succession  of  extinc- 
tion of  species,  and  creation  of  new  ones,  going  on  perpetually  now,  and 
through  an  indefinite  period  of  the  past,  and  to  continue  for  ages  to 
come,  all  in  accommodation  to  the  changes  which  must  continue  in  the 
inanimate  and  habitable  earth,  the  idea  struck  me  as  the  grandest 
which  I  had  ever  conceived,  so  far  as  regards  the  attributes  of  the 
Presiding  Mind."— From  a  letter  of  Sir  Charles  Lyell  to  Sir  John 
Herschel,  1836. 

1  See  Joseph  Le  Conte,  Relation  of  Evolution  to  Materialism,  chap.  iii. 

2  From  R.  S.  Lull,  Organic  Evolution  (The  Macmilhin  Compan}-.  Reprinted 
by  permission). 

3 


4  READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

*'It  is  interesting  to  contemplate  a  tangled  bank,  clothed  with 
many  plants  of  many  kinds,  with  birds  singing  on  the  bushes,  with 
various  insects  flitting  about,  and  with  worms  crawling  through  the 
damp  earth,  and  to  reflect  that  these  elaborately  constructed  forms, 
so  different  from  each  other,  and  dependent  upon  each  other  in  so  com- 
plex a  manner,  have  all  been  produced  by  laws  acting  around  us. 
These  laws,  taken  in  the  largest  sense,  being  Growth  with  Reproduc- 
tion ;  Inheritance  which  is  almost  implied  by  reproduction ;  Variability 
from  the  indirect  and  direct  action  of  the  condition  of  hfe,  and 
from  use  and  disuse;  a  Ratio  of  Increase  so  high  as  to  lead  to  a  struggle 
for  Life,  and  as  a  consequence  to  Natural  Selection,  entailing  Diver- 
gence of  Character  and  the  Extinction  of  less-improved  forms.  Thus, 
from  the  war  of  nature,  from  famine  and  death,  the  most  exalted 
object  which  we  are  capable  of  conceiving,  namely,  the  production  of 
the  higher  animals,  directly  follows.  There  is  a  grandeur  in  this  view 
of  life,  with  its  several  powers,  having  been  originally  breathed  by  the 
Creator  into  a  few  forms  or  into  one;  and  that,  while  this  planet  has 
gone  cycling  on  according  to  the  fixed  law  of  gravity,  from  so  simple  a 
beginning  endless  forms  most  beautiful  and  most  wonderful  have  been, 
and  are  being  evolved. " — Charles  Darwin,  Origin  of  Species,  conclud- 
ing paragraph. 

''Speaking  broadly  we  find  as  a  fact  that  transmutation  of  species 
through  the  geologic  ages  has  been  accompanied  by  increasing  diver- 
gence of  type,  by  the  increased  specialization  of  certain  forms,  and  by 
the  closer  and  closer  adaptation  to  conditions  of  life  on  the  part  of  the 
forms  most  highly  specialized,  the  more  perfect  adaptation  and  the 
more  elaborate  specialization  being  associated  with  the  greatest 
variety  or  variation  in  the  environment.  Accepting  for  this  process 
the  name  organic  evolution,  Herbert  Spencer  has  deduced  from  it  the 
general  law,  that  as  life  endures  generation  after  generation,  its 
character,  as  shown  in  structure  and  function,  undergoes  constant 
differentiation  and  specialization.  In  this  view,  the  transmutation 
of  species  is  not  merely  an  observed  process,  but  a  primitive  necessity 
involved  in  the  very  organization  of  life  itself." — D.  S.  Jordan  and 
V.  L.  Kellogg,  Evolution  and  Animal  Life  (1908),  p.  4. 

''The  Doctrine  of  Evolution  is  a  body  of  principles  and  facts  con- 
cerning the  present  condition  and  past  history  of  the  living  and  lifeless 
things  that  make  up  the  universe.    It  teaches  that  natural  processes 


INTRODUCTION  5 

have  gone  on  in  the  earlier  ages  of  the  world  as  they  do  to-day,  and 
that  natural  forces  have  ordered  the  production  of  all  things  about 
which  we  know."— Henry  Edward  Crampton,  The  Doctrine  oj Evolu- 
tion (1911),  p.  I. 

''Evolution  is  the  gradual  development  from  the  simple  unorgan- 
ized condition  of  primal  matter  to  the  complex  structure  of  the  physi- 
cal universe;  and  in  like  manner,  from  the  beginning  of  organic  life 
on  the  habitable  planet,  a  gradual  unfolding  and  branching  out  into 
all  the  varied  forms  of  beings  which  constitute  the  animal  and  plant 
kingdoms.  The  first  is  called  Inorganic,  the  last  Organic  Evolution. " 
— Richard  Swann  Lull,  Organic  Evolution  (191 7),  p.  6. 

THE   MODERN  ATTITUDE   AS   TO   THE   TRUTH   OF   THE 
EVOLUTION  DOCTRINE 

"Among  that  public  which,  though  educated  and  intelligent,  is 
not  yet  professionally  scientific,  there  has  been,  of  late,  a  widespread 
belief  that  naturalists  have  become  very  doubtful  as  to  the  truth  of  the 
theory  of  evolution  and  are  casting  about  for  some  more  satisfactory 
substitute,  which  shall  better  explain  the  infinitely  varied  and  mani- 
fold character  of  the  organic  world.  This  belief  is  an  altogether  mis- 
taken one,  for  never  before  have  the  students  of  animals  and  plants 
been  so  nearly  unanimous  in  their  acceptance  of  the  theory  as  they  are 
to-day.  It  is  true  that  there  are  still  some  dissentient  voices,  as  there 
have  been  ever  since  the  pubHcation  of  Darwin's  'Origin  of  Species,' 
but  the  whole  trend  of  scientific  opinion  is  strongly  in  favor  of  the 
evolutionary  hypothesis." — ^William  Berryman  Scott,  The  Theory  of 
Evolution,  p.  I. 

"But  the  biological  sciences  were  still  slower  [than  the  physical 
sciences]  to  come  to  their  true  position  as  dignified  science.  Here  was 
the  last  stronghold  of  the  supernaturalist.  Thrust  out  from  the  field 
of  'physical  science'  it  was  in  the  phenomena  of  life  that  the  last  stand 
was  made  by  those  who  claim  that  supernatural  agency  intervenes  in 
nature  in  such  a  way  as  to  modify  the  natural  order  of  events.  When 
Darwin  came  to  dislodge  them  from  this,  their  last  intrenchment,  there 
was  a  fight,  intense  and  bitter,  but,  like  all  attempts  lo  stay  the  prog- 
ress of  human  knowledge,  this  final  struggle  of  the  supernaturalists 
was  foredoomed  to  failure.  The  theory  of  evolution  has  taken  its 
place  beside  the  other  great  conceptions  of  natural  relations,^  and 
largely  through  its  establishment  biology  has  become  truly  a  science 


6  READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

with  a  large  group  of  phenomena  consistently  arranged  and  properly 
classified.  The  discussion  which  followed  the  publication  of  Darwin's 
'Origin  of  Species '  lasted  for  nearly  a  generation,  but  it  is  now  practi- 
cally closed,  so  far  as  any  attempt  to  discredit  evolution  as  a  true 
scientific  generalization  is  concerned.  Scientists  are  no  longer  ques- 
tioning the  fact  of  evolution ;  they  are  busied  rather  with  the  attempt 
to  further  explore  and  more  perfectly  understand  the  operation  of  the 
factors  that  are  at  work  to  produce  that  development  of  animals  and 
plants  which  we  call  organic  evolution." — Maynard  M.  Metcalf,  An 
Outline  of  the  Theory  of  Organic  Evolution  (igii),  pp.  xxii-xxiii. 

"Biologists  turned  aside  from  general  theories  of  evolution  and 
their  deductive  application  to  special  problems  of  descent,  in  order  to 
take  up  objective  experiments  on  variation  and  heredity  for  their  own 
sake.  This  was  not  due  to  any  doubts  concerning  the  reaUty  of 
evolution  or  to  any  lack  of  interest  in  its  problems.  It  was  a  policy 
of  masterly  inactivity  deliberately  adopted;  for  further  discussions 
concerning  the  causes  of  evolution  had  clearly  become  futile  until  a 
more  adequate  and  critical  view  of  existing  genetic  phenomena  had 
been  attained." — E.  B.  Wilson  (address  as  president  of  the  American 
Association  for  the  Advancement  of  Science,  19 14). 

"The  theory  of  development,  as  it  was  revived  by  Darwin  nearly 
half  a  century  ago,  is  in  its  modern  form  prevaiHngly  unhistorical. 
True,  it  has  forced  beneath  its  sceptre  the  m.ethods  of  investigation 
of  all  the  sciences  which  deal  with  the  living  world  and  to-day  almost 

completely  controls  scientific  thought And  yet  science  does 

not  sincerely  rejoice  in  its  conquests.  Only  a  few  incorrigible  and 
uncritically  disposed  optimists  steadfastly  proclaim  what  glorious 
progress  we  have  made;  otherwise,  in  scientific  as  in  lay  circles,  there 
prevails  a  widespread  feeling  of  uncertainty  and  doubt.  Not  as 
though  the  correctness  of  the  principle  of  descent  were  seriously 
questioned;  rather  does  the  conviction  steadily  grow  that  it  is 
indispensable  for  the  comprehension  of  living  nature,  indeed  self- 
evident." — Gustav  Steinmann  (translated  by  W.  B.  Scott  from 
Die  Abstammungslehre  [1908],  pp.  1-2). 

"The  many  converging  lines  of  evidence  point  so  clearly  to  the 
central  fact  of  the  origin  of  forms  of  life  by  an  evolutionary  process 
that  we  are  compelled  to  accept  this  deduction,  but  as  to  almost  all 
the  essential  features,  whether  of  cause  or  of  mode,  by  which  specific 


INTRODUCTION 


diversity  has  become  what  we  perceive  it  to  be,  we  have  to  confess  an 
ignorance  nearly  total." — William  Bateson,  Problems  of  Genetics 
(1913),  p.  248. 

''The  demonstration  of  evolution  as  a  universal  law  of  living 
nature  is  the  great  intellectual  achievement  of  the  nineteenth  century. 
Evolution  has  outgrown  the. rank  of  a  theory,  for  it  has  won  a  place 
in  natural  law  beside  Newton's  law  of  gravitation,  and  in  one  sense 
holds  a  still  higher  rank,  because  evolution  is  the  universal  master, 
while  gravitation  is  among  its  many  agents.  Nor  is  the  law  of  evolu- 
tion any  longer  to  be  associated  with  any  single  name,  not  even  with 
that  of  Darwin,  who  was  its  greatest  exponent.  It  is  natural  that 
evolution  and  Darwinism  should  be  closely  connected  in  many  minds, 
but  we  must  keep  clear  the  distinction  that  evolution  is  a  law,  while 
Darwinism  is  merely  one  of  the  several  ways  of  interpreting  the  work- . 
ings  of  this  law. 

''In  contrast  to  the  unity  of  opinion  on  the  law  of  evolution  is  the 
wide  diversity  of  opinion  on  the  causes  of  evolution.  In  fact,  the 
causes  of  the  evolution  of  life  are  as  mysterious  as  the  law  of  evolution 
is  certain.  Some  contend  that  we  already  know  the  chief  causes  of 
evolution,  others  contend  that  we  know  little  or  nothing  of  ihem. 
In  this  open  court  of  conjecture,  of  hypothesis,  of  more  or  less  heated 
controversy  the  names  of  Lamarck,  of  Darwin,  of  Weismann  figure 
prominently  as  leaders  of  different  schools  of  opinion;  while  there  are 
others,  like  myself,  who  for  various  reasons  belong  to  no  school,  and 
are  as  agnostic  about  Lamarckism,  as  they  are  about  Darwinism  or 
Weismannism,  or  the  more  recent  form  of  Darwinism,  termed  Muta- 
tion by  De  Vries. 

"In  truth,  from  the  period  of  the  earlier  stages  of  Greek  thought 
man  has  been  eager  to  discover  some  natural  cause  of  evolution,  and 
to  abandon  the  idea  of  supernatural  intervention  in  the  order  of 
nature.  Between  the  appearance  of  The  Origin  of  Species,  in  1859, 
and  the  present  time  there  have  been  great  waves  of  faith  in  one 
explanation  and  then  in  another:  each  of  these  waves  of  confidence 
has  ended  in  disappointment,  until  finally  we  have  reached  a  stage 
of  very  general  scepticism.  Thus  the  long  period  of  evolution,  experi- 
ment, and  reasoning  which  began  with  the  French  natural  philosopher, 
Buffon,  one  hundred  and  fifty  years  ago,  ends  in  1916  with  the  general 
feeling  that  our  search  for  causes,  far  from  being  near  completion,  has 
only  just  begun. 


8  READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

''Our  present  state  of  opinion  is  this:  we  know  to  some  extent 
how  plants  and  animals  and  man  evolve;  we  do  not  know  why  they  v, 
evolve.  We  know,  for  example,  that  there  has  existed  a  more  or  less 
complete  chain  of  beings  from  nomad  to  man,  that  the  one-toed  horse 
had  a  four-toed  ancestor,  that  man  has  descended  from  an  unknown 
ape-like  form  somewhere  in  the  Tertiary.  We  know  not  only  those 
larger  chains  of  descent,  but  many  of  the  minute  details  of  these 
transformations.  We  do  not  know  their  internal  causes,  for  none  of 
the  explanations  which  have  in  turn  been  offered  during  the  last  hun- 
dred years  satisfies  the  demands  of  observation,  of  experiment,  of 
reason.  It  is  best  frankly  to  acknowledge  that  the  chief  causes  of  the 
orderly  evolution  of  the  germ  are  still  entirely  unknown,  and  that  our 
search  must  take  an  entirely  fresh  start." — H.  F.  Osborn,  The  Origin 
and  Evolution  of  Life  (Charles  Scribner's  Sons),  1918,  pp.  viii-x. 

WHAT   ORGANIC   EVOLUTION  IS   NOT 

[i.  The  evolution  doctrine  is  not  a  creed  to  be  accepted  on  faith, 
as  are  religious  faiths  or  creeds.  It  appeals  entirely  to  the  logical 
faculties,  not  to  the  spiritual,  and  is  not  to  be  accepted  until  proved. 

2.  It  does  not  teach  that  man  is  a  direct  descendant  of  the  apes 
and  monkeys,  but  that  both  man  and  the  modern  apes  and  monkeys 
have  been  derived  from  some«as  yet  unknown  generalized  primate 
ancestor  possessing  the  common  attributes  of  all  three  groups  and 
lacking  their  specializations. 

3.  It  is  not  synonymous  with  Darwinism,  for  the  latter  is  merely 
one  man's  attempt  to  explain  how  evolution  has  occurred. 

4.  Contrary  to  a  very  widespread  idea,  evolution  is  by  no  means 
incompatible  with  religion.  Witness  the  fact  that  the  early  Christian 
Theologians,  Augustine  and  Thomas  Aquinas,  were  evolutionists,  and 
the  majority  of  thoughtful  theologians  of  all  creeds  are  today  in 
accord  with  the  evolution  idea,  many  of  them  even  applying  the  prin- 
ciple to  their  studies  of  religion;  for  religious  ideas  and  ideals,  like 
other  human  characters,  have  evolved  from  crude  beginnings  and  are 
still  undergoing  processes  of  refinement. 

5.  The  evolution  idea  is  not  degrading.  Quite  the  contrary;  it  is 
ennobling  as  is  well  brought  out  by  the  classic  statement  of  Darwin 
on  page  4  and  by  that  of  Lyell,  on  page  3. 

6.  The  evolution  doctrine  does  not  teach  that  man  is  the  goal  of 
all  evolutionary  process,  but  that  man  is  merely  the  present  end 
product  of  one  particular  series  of  evolutionary  changes.     The  goal 


INTRODUCTION  9 

of  evolution  in  general  is  perfection  of  adaptation  to  the  conditions  of 
life  as  they  happen  to  be  at  any  particular  time.  Many  a  highly 
perfected  creature  has  reached  the  goal  of  its  evolutionary  course 
only  to  perish  because  it  was  too  highly  perfected  for  a  particular 
environment  and  could  not  withstand  the  hardships  incident  to  radi- 
cally changed  world-conditions.  Many  evolutions  therefore  have 
been  completed,  while  others  are  still  awaiting  the  opportunity  to 
speed  up  toward  a  new  goal. 

7.  Evolution  is  therefore  not  entirely  a  thing  of  the  past.  Obvi- 
ously some  species,  including  Man  perhaps,  are  nearly  at  the  end 
of  their  physical  evolution,  but  there  are  always  certain  generalized 
plastic  types  awaiting  the  next  great  opportunity  for  adaptive  speciali- 
zation.— Ed.] 


CHAPTER  II 

HISTORICAL  ACCOUNT  OF  THE  DEVELOPMENT  OF  THE 

EVOLUTION  THEORY 

H.  H.  Newman 

The  chief  sources  of  material  for  the  present  chapters  are:  Osborn's 
From  the  Greeks  to  Darwin}  and  Judd's  The  Coming  of  Evolution.'^ 

Professor  Osborn  studies  the  evolution  of  the  evolution  idea  as  a 
biologist  would  investigate  the  evolution  of  a  group  of  species,  using 
all  of  the  available  sources  of  evidence  at  his  disposal.  The  fragments 
of  ancient  writing  and  the  crude  imaginings  of  early  natural  philoso- 
phers are  the  fossils  of  the  evolution  idea,  many  of  them  ancestors 
of  modern  principles;  fragments  of  ancient  or  discarded  ideas  that 
still  persist,  though  irrelevant  to  modern  thought,  are  the  vestigial 
structures  that  proclaim  kinship  between  the  past  and  the  present; 
parallelisms  between  the  development  of  ideas  in  the  minds  of  inde- 
pendent thinkers  do  not  prove  plagiarism,  but  indicate  common 
descent  from  the  same  ancestral  ideas. 

This  whole  history  is  an  important  chapter  in  the  story  of  human 
evolution  in  general,  for  it  deals  with  the  evolution  of  a  characteristic 
human  faculty — that  of  appreciating  the  broad  relations  that  exist 
between  the  past  and  the  present.  This  faculty  has  evolved  as  truly 
as  has  an  organic  system  such  as  the  nervous  system,  and  is  unques- 
tionably closely  bound  up  with  the  latter. 

The  evolution  theory  is  a  vast  fabric  of  interrelated  and  inter- 
dependent facts  and  principles.  The  fabric  has  been  gradually  woven 
out  of  separate  threads  and  now  stands  strong  though  flexible,  with 
strands  reaching  into  all  sciences  and  tending  to  unify  all  science. 

It  was  only  after  the  lesser  ideas  came  to  be  clearly  apprehended 
that  it  was  possible  for  the  master  minds  of  Lamarck  and  of  Darwin  to 
weave  them  together  into  a  consistent  fabric  and  to  bring  the  facts 
together  under  the  one  great  conception,  that  of  organic  evolution. 
Classification  was  a  science,  comparative  anatomy  had  made  much 
progress,  the  principles  of  embryology  were  fairly  well  understood, 

"■  H.  F.  Osborn,  From  the  Greeks  to  Darwin  (The  Macmillan  Company,  1908). 
»  John  W.  Judd,  The  Coming  of  Evolution  (Cambridge  University  Press,  191 1). 

10 


HISTORICAL  ACCOUNT  OF  EVOLUTION  THEORY  ii 

much  palaeontological  discovery  had  been  made,  before  it  was  found 
that  the  facts  from  these  sources  all  pointed  to  one  general  principle, 
and  only  one,  that  master-principle  "organic  evolution." 

We  shall  now  trace  the  development  of  the  evolution  idea  from 
its  inception  among  the  Greeks  to  its  present  status,  and  shall  first 
give  a  brief  account  of  Greek  evolution. 

EVOLUTION  AMONG   THE   GREEKS 

The  early  Greek  thinkers  were  sea  people.  ''Along  the  shores  and 
in  the  waters  of  the  blue  Aegean,"  says  Osborn,  "teeming  with  what 
we  now  know  to  be  the  earliest  and  simplest  forms  of  animals  and 
plants,  they  founded  their  hypotheses  as  to  the  origin  and  succession 

of  life The  spirit  of  the  Greeks  was  vigorous  and  hopeful. 

Not  pausing  to  test  their  theories  by  research,  they  did  not  suffer  the 
disappointments  and  delays  which  come  from  one's  own  efforts  to 
wrest  truths  from  Nature. " 

The  Greeks  were  anticipators  of  Nature.  Their  speculations  out- 
stripped the  facts;  in  fact  were  usually  made  with  "eyes  closed  to  the 
facts."  Their  theories  were  inextricably  bound  up  with  current 
mythology,  were  naive,  vague,  and,  from  our  modern  point  of  view, 
ridiculous;  yet  they  contained  many  grains  of  truth  and  were  the 
germs  out  of  which  grew  the  saner  ideas  of  subsequent  thinkers, 

Thales  (624-548  B.C.)  was  the  first  of  the  Greeks  to  theorize  about 
the  origin  of  life.  "He  looked  upon  the  great  expanse  of  mother  ocean 
and  declared  water  to  be  the  mother  from  which  all  things  arose,  and 
out  of  which  they  exist."  This  idea  anticipates  the  modern  idea  of 
the  aquatic  or  marine  origin  of  life,  and  also  the  present  idea  as  to  the 
indispensability  of  water  in  all  vital  processes. 

Anaximander  (611-547  B.C.)  has  been  called  the  prophet  of 
Lamarck  and  of  Darwin.  While  his  theories  were  highly  mythical  in 
character,  he  conceived  the  idea  of  a  gradual  evolution  from  a  formless 
or  chaotic  condition  to  one  of  organic  coherence.  He  saw  vaguely  the 
idea  of  transformation  of  aquatic  species  into  terrestrial,  even  deriving 
man  from  aquatic  fishlike  men  (mythical  mermen)  who  were  able  to 
emerge  from  the  water  only  after  they  had  undergone  the  necessary 
changes  required  for  land  life.  This  idea  involves  that  of  adaptation, 
one  of  the  cornerstones  of  the  modern  evolutionary  structure. 

Anaximenes  (588-524  B.C.),  a  pupil  of  Anaximander,  "found  in  air 
the  cause  of  all  things.  Air,  taking  the  form  of  soul,  imparts  life, 
motion,  and  thought  to  animals. "     It  is  questionable  whether  this  is  a 


12        READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

prophecy  of  the  importance  of  oxygen  and  oxidation  in  vital  processes. 
Anaximenes  also  introduced  the  idea  of  abiogenesis  (spontaneous 
generation  of  living  substance),  his  idea  being  that  animals  and  plants 
arose  out  of  a  primordial  terrestrial  slime  wakened  into  life  by  the  sun's 
heat.  This  primordial  terrestrial  slime  is  perhaps  a  prophecy  of 
Oken's  "Urschleim"  or  of  protoplasm. 

Xenophanes  (576-480  B.C.),  probably  another  pupil  of  Anaxi- 
mander,  ''agreed  with  his  master  so  far  as  to  trace  the  origin  of  man 
back  to  the  transition  period  between  the  fluid  or  water  and  solid  or 
land  stages  of  the  development  of  the  earth."  He  was  the  first  to 
recognize  fossils  as  the  remains  of  animals  once  alive,  and  to  see 
in  them  proof  that  once  the  seas  covered  the  entire  surface  of  the 
earth. 

Heraclitus  (535-475  B.C.),  the  first  of  a  group  of  physicists,  was  the 
great  proponent  of  the  philosophy  of  change.  He  was  imbued  with 
the  idea  that  all  was  motion,  that  nothing  was  fixed.  "Everything 
was  perpetually  transposed  into  new  shapes."  Although  HeracUtus 
did  not  apply  his  ideas  to  living  creatures  and  their  evolutions,  his 
philosophy  was  influential  in  molding  the  ideas  of  his  successors. 

Empedocles  (495-435  B.C.) ''  took  a  great  stride  beyond  his  predeces- 
sors, and  may  justly  be  called  the  father  of  the  Evolution  idea 

He  beHeved  in  Abiogenesis,  or  spontaneous  generation,  as  the  explana- 
tion of  the  origin  of  life,  but  that  Nature  does  not  produce  the  lower 
and  higher  forms  simultaneously  or  without  an  effort.  Plant  life 
comes  first,  and  animal  life  developed  only  after  a  long  series  of  trials." 
He  thought  that  all  creatures  arose  through  the  fortuitous  combina- 
tion of  scattered  and  miscellaneous  parts  which  were  attracted  or 
repelled  by  the  forces  of  love  or  hate  (the  two  great  forces  in  Nature). 
Thus  arose  every  sort  of  combination  of  parts,  some  more  or  less  har- 
monious and  complete,  others  with  ill-assorted  organization,  lacking 
in  some  parts,  double  or  triple  in  others.  Some  of  these  combinations 
could  not  survive,  because  of  their  incompleteness  and  incongruity, 
but  ''other  forms  arose  which  were  able  to  support  themselves  and 
multiply."  This  is  a  sort  of  vague  prophecy  of  the  survival  of  the 
fittest  or  of  natural  selection.  Four  sparks  of  truth  may  be  found  in 
Empedocles'  philosophy,  "first,  that  the  development  of  life  was  a 
gradual  process;  second,  that  plants  were  evolved  before  animals; 
third,  that  imperfect  forms  were  gradually  replaced  (not  succeeded) 
by  perfect  forms;  fourth,  that  the  natural  cause  of  the  production  of 
perfect  forms  was  the  extinction  of  the  imperfect." 


HISTORICAL  ACCOUNT  OF  EVOLUTION  THEORY  13 

Democritus  (b.450  B.C.),  said  to  have  been  the  first  comparative 
anatomist,  contributed  to  the  substructure  of  evolution  the  idea  of  the 
''adaptation  of  single  structures  and  organs  to  certain  purposes." 

Anaxagoras  (500-428  B.C.)  was  the  first  of  the  Greeks  ''  to  attribute 
the  adaptations  of  Nature  to  Intelligent  Design,  and  was  thus  the 
founder  of  Teleology,"  an  idea  that  has  played  a  retarding  function  in 
the  history  of  evolution. 

"With  Aristotle  (384-322  B.C.)  we  enter  a  new  world,"  says  Osborn. 
*'He  towered  above  his  predecessors,  and  by  the  force  of  his  genius 
created  Natural  History."  The  evolution  idea  took  a  great  step 
forward  with  Aristotle  and  reached  a  stage  beyond  which  it  did  not 
go  for  many  centuries.  He  covered  nearly  the  whole  field,  touching 
upon  most  of  the  foundation  stones  of  the  complex  problem.  His 
ideas,  like  those  of  all  the  Greeks,  were  often  vague  and,  in  the  light 
of  present  knowle'dge,  incoherent;  but,  considering  the  meager  factual 
background  with  which  he  had  to  work  he  had  a  surprising  grasp  of 
the  whole  situation.     Some  of  his  principal  ideas  were: 

1.  He  had  a  clear  idea  of  laws  of  Nature  (''Necessity"),  and 
attributed  all  evolutionary  changes  to  natural  causes. 

2.  He  opposed  the  ideas  of  Empedocles  as  to  the  fortuitous  origin 
of  adaptive  characters,  and  favored  the  idea  of  intelligent  design  in 
nature.     He  was  therefore  a  teleologist. 

3.  Hence  he  rejected  the  hypothesis  of  the  survival  of  the  fittest, 
because  it  was  based  on  chance. 

4.  He  "had  substantially  the  modern  conception  of  the  Evolution 
of  Hfe,  from  a  primordial  soft  mass  of  living  matter. " 

5.  He  had  an  idea  of  a  linear  phylogenetic  series,  beginning 
with  plants,  then  plant-animals,  such  as  sponges  and  sea  anemones, 
then  animals  with  sensibility,  and  thence  by  graded  stages  up  to 
Man. 

6.  "He  perceived  the  unity  of  type  in  certain  classes  of  animals, 
and  considered  rudimentary  organs  as  tokens  whereby  Nature  sustains 
this  unity. " 

7.  "He  anticipated  Harvey's  doctrine  of  Epigenesis  in  embryonic 
development." 

8.  "He  fully  perceived  the  forces  of  hereditary  transmission,  of  the 
prepotency  of  one  parent  or  stock,  and  of  Atavism  and  Reversion. " 

9.  He  is  the  father  of  that  ancient  fallacy  called  "prenatal  influ- 
ences," and  believed  in  the  inheritance  of  acquired  characters,  as  is 
shown  in  the  following  passage : 


14        READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

"  Children  resemble  their  parents  not  only  in  congenital  characters, 
but  in  those  acquired  later  in  life.  For  cases  are  known  where  parents 
have  been  marked  by  scars  and  children  have  shown  traces  of  these 
scars  at  the  same  points;  a  case  is  also  reported  from  Chalcedon  in 
which  a  father  had  been  branded  with  a  letter,  and  the  same  letter 
somewhat  blurred  and  not  sharply  defined  appeared  upon  the  arm  of 
the  child." 

POST-ARISTOTELIANS 

With  Aristotle  the  evolution  idea  reached  a  high  watermark  and 
thereafter  the  tide  steadily  declined.  Pliny,  Epicurus,  Lucretius,  and 
others  kept  the  idea  alive,  but  added  nothing  of  importance  to 
Aristotle's  contribution. 

Lucretius  (99-55  B.C.)  appears  to  have  been  chiefly  a  follower  of 
Empedocles  in  so  far  as  his  ideas  as  to  the  origin  of  animals  are  con- 
cerned. He  ignored  Aristotle  and  his  much  more  advanced  phi- 
losophy of  Nature,  finding  the  earlier,  more  mythical  conceptions 
better  suited  to  poetic  expression.  He  was  not  truly  an  evolutionist, 
for  he  believed  that  all  animals  and  plants  arose  fully  formed  from  the 
earth.  Lucretius  is  of  importance  chiefly  as  a  retarding  factor,  for 
his  ideas  were  accepted  and  admired  even  up  to  the  eighteenth  century; 
witness  Milton's  immortal  verse: 

''The  Earth  obey'd,  and  straight, 
Op'ning  her  fertile  womb,  teem'd  at  a  birth 
Innumerous  living  creatures,  perfect  forms, 
Limb'd  and  full  grown. " 

THE   EARLY   THEOLOGIANS 

The  evolution  idea  made  no  progress  from  the  time  of  Aristotle 
until  the  revival  of  learning  in  the  Middle  Ages.  The  chief  inhibiting 
factor  was  the  church,  which  favored  traditional  knowledge  and  the 
special-creation  idea  in  its  most  literal  form.  Yet  the  early  theo- 
logians, such  as  Gregory,  Augustine,  and  Thomas  Aquinas,  were  open- 
minded  about  the  evolution  idea  and  attempted  to  reconcile  it  with 
the  scriptural  account  of  creation. 

''Gregory  of  Nyssa  (331-396  a.d.)  taught,"  says  Osborn,  ''that 
Creation  was  potential.  God  imparted  to  matter  its  fundamental 
properties  and  laws.  The  objects  and  completed  forms  of  the  Universe 
developed  gradually  out  of  chaotic  material. " 


HISTORICAL  ACCOUNT  OF  EVOLUTION  THEORY         '      15 

Augustine  (353-430  a.d.)  conceived  the  idea,  now  so  generally 
adopted  by  theologians,  that  the  biblical  account  of  creation  is  alle- 
gorical. "In  explaining  the  passage  'In  the  beginning  God  created 
heaven  and  the  earth,'  he  says: 

"In  the  beginning  God  made  the  heaven  and  the  earth,  as  if  this 
were  the  seed  of  the  heaven  and  the  earth,  although  as  yet  all  the 
matter  of  heaven  and  of  earth  was  in  confusion,  but  because  it  was 
certain  that  from  this  the  heaven  and  the  earth  would  be,  therefore 
the  material  itself  is  called  by  that  name. " 

Thomas  Aquinas  (1225-74),  who  wrote  much  later  and  was  one  of 
the  leading  church  authorities,  satisfied  himself  with  merely  expound- 
ing Augustine:  "As  to  the  production  of  plants,  Augustine  holds  a 
different  view,  ....  for  some  say  that  on  the  third  day  plants  were 
actually  produced,  each  in  its  kind — a  view  favoured  by  the  superficial 
reading  of  Scripture.  But  Augustine  says  that  the  earth  is  then  said 
to  have  brought  forth  grass  and  trees  Qausaliter;  that  is,  it  then 
received  the  power  to  produce  them.  For  in  those  first  days  .... 
God  made  creation  primarily  or  causaliter,  and  then  rested  from  His 
work." 

THE   REVIVAL   OF   SCIENCE 

During  the  long  centuries  until  the  awakening  of  science  in  the 
Middle  Ages  the  evolution  idea  smouldered  along  in  the  minds  of  a 
few  thinkers,  but  it  was  only  when  a  few  daring  spirits  broke  the 
trammels  of  scholasticism  and  began  once  more  to  give  free  rein  to 
observation  and  speculation  that  the  idea  once  more  burst  into  flame 
and  began  its  second  great  period  of  advance. 

A  small  group  of  natural  philosophers,  scarcely  more  scientific 
in  their  methods  than  the  Greeks,  were  the  first  to  revive  interest  in 
the  evolution  idea.  Of  these  the  names  of  Bacon,  Descartes,  Leib- 
nitz, and  Kant  are  the  most  famous. 

Francis  Bacon  (1561-1626)  did  much  to  revive  the  vogue  of  Aris- 
totelian ideas.  He  also  added  some  new  ideas:  (i)  that  the  muta- 
bility of  species  was  the  result  of  the  accumulation  of  variations;  (2) 
that  variations  of  an  extreme  kind,  equivalent  to  "mutations,"  some- 
times occur;  (3)  that  new  species  might  arise  by  a  degenerative 
process  from  old  species. 

Emanuel  Kant  (17  24-1 804)  was  purely  a  philosopher,  not  an 
observing  naturalist,  but  he  profited  by  the  writings  of  the  contem- 
porary naturalists,  especially  those  of  Buff  on  and  Maupertius.    His 


l5        READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

general  ideas  of  evolution  were  comprehensive  and  summed  up  the 
best  features  of  all  preceding  writers,  but  he  did  not  contribute  any- 
thing new  to  the  pressing  problem  of  the  causes  of  evolution. 

Real  progress  was  not  to  be  made  through  further  speculation. 
What  was  most  needed  was  facts,  and  it  was  the  task  of  the  naturalists 
to  furnish  these.  The  earliest  of  the  eighteenth-century  naturalists 
were  still  anticipators  of  Nature  in  that  their  theories  outran  their 
facts.     Of  these  the  names  of  Bonnet  and  Oken  are  the  best  known. 

Bonnet  (1720-93)  was  an  evolutionist  only  in  the  sense  that  he 
believed  that  the  adult  organism  is  present  in  the  egg  and  evolves  from 
it  by  a  process  of  unfolding  or  expansion.  He  was  a  zoological 
observer  of  some  note,  however,  and  made  some  of  the  most  important 
contributions  of  his  time  to  the  general  subject.  He  believed  "that 
the  globe  had  been  the  scene  of  great  revolutions,  and  that  the  chaos 
described  by  Moses  was  the  closing  chapter  of  one  of  these;  thus  the 
Creation  described  in  Genesis  may  be  only  a  resurrection  of  animals 
previously  existing."  This  theory  admits  of  no  progress  and  is 
scarcely  worthy  of  the  name  evolution. 

Oken  (1776-1851)  is  known  chiefly  for  his  "Urschleim"  doctrine 
and  his  ideas  of  cells  as  vesicular  units  of  life.  According  to  him, 
"Every  organic  thing  has  arisen  out  of  slime  and  is  nothing  but  slime 
in  various  forms.  This  primitive  slime  originated  in  the  sea  from 
inorganic  matter."  These  ideas  are  purely  speculative,  but  suggest 
our  modern  ideas  of  protoplasm  and  cells. 

THE    GREAT  NATURALISTS   OF   THE   EIGHTEENTH   CENTURY 

Three  great  names  stand  out  above  all  the  rest  during  this  period : 
those  of  Linnaeus,  Buffon,  and  Erasmus  Darwin. 

Linnaeus  (1707-78)  was  the  father  of  taxonomy.  He  contributed 
facts  rather  than  theories;  he  invented  our  present  system  of  binomial 
nomenclature  of  both  animals  and  plants,  and  a  great  many  of  his 
generic  and  specific  names  still  persist.  Unfortunately  he  was  an 
ardent  advocate  of  the  special-creation  idea,  holding  that  all  of  the 
true  species  were  created  as  they  are  known  today,  except  that  new 
combinations  may  have  arisen  through  hybridization  or  through 
degeneration.  His  influence  wasgreat,  but  was  reactionary  and  proved 
a  serious  hindrance  to  the  progress  of  the  evolution  idea. 

Btiffon  (1707-88),  born  the  same  year  as  Linnaeus,  has  been 
recognized  as  the  father  of  the  modern  applied  form  of  the  evolution 
idea.     He  attempted  to  explain  particular  cases  on  an  evolutionary 


HISTORICAL  ACCOUNT  OF  EVOLUTION  THEORY  17 

basis.  He  lived  at  a  time  when  it  was  dangerous  to  express  views  that 
might  be  interpreted  as  unorthodox,  and  this  may  account  for  the 
apparent  lack  of  conviction  in  his  own  ideas;  for  he  wavered  between 
special  creation  and  evolution.  His  chief  contribution  is  the  idea  of 
the  direct  influence  of  the  environment  in  the  modification  of  the 
structure  of  animals  and  plants  and  the  conservation  of  these  modifi- 
cations through  heredity.  This  seems  to  imply  that  he  believed  in 
the  inheritance  of  acquired  characters.  He  expressed  himself  as 
believing  that  climate  has  had  a  direct  effect  in  the  production  of 
various  races  of  man,  that  new  varieties  of  animals  have  been  formed 
through  human  intervention  (an  idea  implying  artificial  selection), 
that  similar  results  are  produced  by  geographic  migration  and  through 
isolation.  He  expressed  the  view  that  there  is  a  great  struggle  for 
existence  among  animals  and  plants  to  prevent  overcrowding  and 
to  maintain  the  balance  of  Nature.  This  appears  to  be  an  anticipation 
of  Malthus'  ideas  on  population,  which  were  so  influential  in  shaping 
the  theories  of  Charles  Darwin  and  of  Wallace. 

While  many  of  his  ideas  appear  to  be  highly  advanced  for  his  time, 
his  special  applications  are  open  to  serious  criticism.  He  reasons, 
for  example,  that  the  pig  as  it  exists  at  present  could  not  have  been 
formed  on  any  original  complete  and  perfect  plan,  but  seems  to  have 
been  formed  as  a  compound  from  other  animals.  It  has  useless  parts 
which  could  hardly  have  been  a  part  of  a  perfect  plan  as  originally 
conceived.  He  thought  that  "the  ass  is  a  degenerate  horse,  and  the 
ape  a  degenerate  man. " 

On  the  whole  Buff  on  was  not  a  strong  advocate  of  evolution  and 
his  influence  was  far  from  being  as  important  as  some  recent  writers 
appear  to  believe. 

Erasmus  Darwin  (1731-1802),  grandfather  of  Charles  Darwin, 
was  a  physician,  a  naturalist,  and  a  minor  poet.  Undoubtedly  he 
transmitted  to  his  grandson  his  thoughtful  habit  and  love  of  science 
and  was  influential  in  shaping  his  ideas  on  evolution.  The  elder 
Darwin's  theories  as  to  the  causes  of  evolution  closely  paralleled 
those  of  Lamarck,  his  distinguished  contemporary  in  France,  but  it 
is  now  very  generally  conceded  that  the  ideas  of  the  two  men  were 
independently  derived  from  similar  materials.  Erasmus  Darwin  laid 
little  emphasis  on  the  direct  action  of  the  environment,  which  had  been 
Buffon's  main  dependence,  and  dwelt  on  the  internal  origin  of  adap- 
tive characters.  ''All  animals,"  he  said,  ''undergo  transformations 
which  are  in  part  produced  by  their  own  exertions,  in  response  to 


1 8        READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

pleasures  and  pains,  and  many  of  these  acquired  forms  or  propensities 
are  transmitted  to  their  posterity."  One  could  ask  for  no  clearer 
statement  of  the  idea  that  acquired  characters  are  inherited. 

The  fierceness  of  the  struggle  for  existence  was  clearly  recognized 
by  Dr.  Darwin.  He  considers  that  this  struggle  is  beneficial  to  Nature 
as  a  whole  because  it  checks  the  too  rapid  increase  of  life.  One  step 
farther  in  the  argument,  and  he  would  have  arrived  at  the  idea  of  the 
survival  of  the  fittest,  but  he  never  took  that  step.  He  agreed  with 
the  early  Christian  fathers  in  his  belief  that  the  powers  of  development 
were  implanted  within  the  first  organisms  by  the  Creator  and  that 
subsequent  evolution  of  adaptive  characters  went  on  without  further- 
divine  intervention.  The  power  of  improvement  rests  within  the 
creature's  own  organizations  and  is  due  to  his  own  efforts.  The 
effects  of  these  efforts,  he  believes,  are  transmitted  to  offspring  so 
that  there  might  be  a  cumulative  effect  throughout  many  generations 
of  the  results  of  effort. 

Erasmus  Darwin  was  perhaps  the  first  to  express  clearly  the  ideas 
that  millions  of  years  have  been  required  for  the  processes  of  organic 
evolution  and  that  all  life  arose  from  one  primordial  protoplasmic 
mass.     He  writes  as  follows: 

"From  thus  meditating  upon  the  minute  portion  of  time  in  which 
many  of  the  above  changes  have  been  produced,  would  it  be  too  bold 
to  imagine,  in  the  great  length  of  time  since  the  earth  began  to  exist, 
perhaps  millions  of  ages  before  the  commencement  of  the  history  of 
mankind,  that  all  warm-blooded  animals  have  arisen  from  one  living 
filament,  which  the  first  great  Cause  imbued  with  animality,  with  the 
power  of  acquiring  new  parts,  attended  with  new  propensities,  directed 
by  irritations,  sensations,  volitions,  and  associations,  and  thus  possess- 
ing the  faculty  of  continuing  to  improve  by  its  own  inherent  activity, 
and  of  delivering  down  these  improvements  by  generation  to  pos- 
terity, world  without  end  ?  " 

LAMARCK 

Lamarck  (1744-182 9),  the  greatest  of  French  evolutionists,  is  now 
looked  upon  as  ''the  founder  of  the  complete  modern  Theory  of 
Descent. "  Osborn  considers  him  ''  the  most  prominent  figure  between 
Aristotle  and  Darwin.  One  cannot  compare  his  Philosophie  zoologique 
with  all  previous  and  contemporary  contributions  to  the  evolution 
theory  or  learn  the  extraordinary  difficulties  under  which  he  laboured, 
and  that  his  work  was  put  forth  only  a  few  years  after  he  had  turned 


HISTORIC.\L  ACCOUNT  OF  EVOLUTION  THEORY  19 

from  Botany  to  Zoology,  without  gaining  the  greatest  admiration  for 
his  genius.  No  one  has  been  more  misunderstood,  or  judged  with  more 
partiality  by  over  or  under  praise.  The  stigma  placed  upon  his  writ- 
ings by  Cuvier,  who  greeted  every  fresh  edition  of  his  words  as  a 
'nouvelle  folie,'  and  the  disdainful  illusions  to  him  by  Charles  Darwin 
(the  only  writer  of  whom  Darwin  ever  spoke  in  this  tone)  long  placed 
him  in  the  light  of  a  purely  extravagant,  speculative  thinker.  Yet, 
as  a  fresh  instance  of  the  certainty  with  which  men  of  science  finally 
obtain  recognition,  it  is  gratifying  to  note  the  admiration  which  has 
been  accorded  to  him  in  Germany  by  Haeckel  and  others,  by  his 
countrymen,  and  by  a  large  school  of  American  and  English  writers 
of  the  present  day;  to  note,  further,  that  his  theory  was  finally  taken 
up  and  defended  by  Charles  Darwin  himself,  and  that  it  forms  the 
very  heart  of  the  system  of  Herbert  Spencer. " 

^        Lamarck's  main  theory  of  evolution  was  expressed  by  him  in  the 

^   form  of  his  four  ''laws": 

I.  ''Life,  by  its  proper  forces,  continually  tends  to  increase  the 
volume  of  every  body  which  possesses  it,  and  to  increase  the  size  of  its 
parts,  up  to  a  limit  which  brings  it  about." 

II.  "The  production  of  a  new  organ  in  the  animal  body  results 
from  the  supervention  of  a  new  want  which  continues  to  make  itself 
felt,  and  a  new  movement  which  this  want  gives  rise  to  and  maintains." 

III.  "The  development  of  organs  and  their  powers  of  action  are 
constantly  in  ratio  to  the  employment  of  these  organs." 

IV.  "Everything  which  has  been  acquired,  impressed  upon,  or 
changed  in  the  organization  of  individuals  during  the  course  of  their 
life  is  preserved  by  generation  and  transmitted  to  new  individuals 
which  have  descended  from  those  which  have  undergone  these 
changes. 

It  is  about  the  last  "  law  "  that  the  controversy  rages,  for  it  upholds 
the  idea  that  acquired  characters  are  inherited,  now  known  as  the 
"Lamarckian  doctrine." 

A  somewhat  more  specific  statement  of  Lamarck's  theory  of 
evolution  may  be  summed  up  in  the  following  list  of  factors  which  he 
considered  as  playing  an  essential  role  in  evolution. 

1.  "Favorable  circumstances  attending  changes  of  environment, 
soil,  food,  temperature,  etc.,  supposed  to  act  directly  in  the  case  of 
plants,  indirectly  in  the  case  of  animals  and  man." 

2.  "Needs,  new  physical  wants  or  necessities  induced  by  the 
changed  conditions  of  life.     Lamarck  believed  that  change  of  habits 


20        READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

may  lead  to  the  origination  or  modification  of  organs;  that  changes 
of  function  also  modify  or  create  new  organs.  By  changes  of  environ- 
ment animals  become  subjected  to  new  surroundings,  involving  new 
ways  and  means  of  living.  Thus,  certain  land  birds,  driven  by  neces- 
sity to  obtain  their  food  in  the  water,  gradually  assumed  characters 
adapting  them  for  swimming,  wading,  or  for  searching  for  food  in  the 
shallow  water,  as  in  the  case  of  the  long-necked  kinds. " 

3.  ''Use  and  disuse.  To  use  an  organ  is  to  develop  it;  not  to  use 
it  is  to  eventually  lose  it.  The  anterior  limbs  of  birds  became  capable 
of  sustained  flight  through  use;  the  hind  limbs  of  whales  are  lost 
through  disuse,  etc." 

4.  ''Competition.  Nature  takes  precautions  not  to  overcrowd 
the  earth.  The  stronger  and  larger  living  things  destroy  the  smaller 
and  weaker.  The  smaller  multiply  very  rapidly,  the  larger  slowly. 
A  physiological  balance  is  maintained.  ■' 

5.  "The  transmission  of  acquired  characters.  The  advantages 
gained  by  every  individual  as  the  result  of  the  structural  changes 
resulting  from  use  or  disuse  are  handed  down  to  its  descendants  who 
begin  where  the  parent  leaves  off,  and  so  are  able  to  continue  the  pro- 
gression or  retrogression  of  the  character." 

6.  "Cross-breeding.  Tf  when  any  peculiarity  of  form  or  any 
defects  whatsoever  are  acquired,  the  individuals  in  this  case,  always 
pairing,  they  will  produce  the  same  peculiarities,  and  if  for  successive 
generations  confined  to  such  unions,  a  special  distinct  race  will  then 
be  formed.  But  perpetual  crosses  between  individuals  which  have 
not  the  same  peculiarities  of  form  result  in  the  disappearance  of  all 
the  peculiarities  acquired  by  the  particular  circumstances.'" 

7.  "Isolation.  'Were  not  man  separated  by  distances  of  habita- 
tion, the  mixtures  resulting  from  crossing  would  obliterate  the  general 
characters  which  distinguish  different  nations.'  This  thought  is 
expressed  in  his  account  of  the  origin  of  men  from  apes,  and  is  not 
applied  to  living  things  in  general. " 

In  addition  to  his  theories  as  to  the  causes  of  evolution,  Lamarck 
was  the  first  to  present  the  idea  of  the  tree  of  life,  or  phylogenic  tree, 
as  a  mode  of  representing  animal  relationships.  All  previous  classifi- 
cations'had  been  based  on  the  idea  of  a  single  linear  phylogenetic 
series,  each  lower  group  being  supposedly  ancestral  to  a  higher  group, 
and  all  in  a  single  chain. 

We  may  best  sum  up  Lamarck's  work  and  influence  in  the  words 
of  Osborn: 


HISTORICAL  ACCOUNT  OF  EVOLUTION  THEORY  21 

''Lamarck,  as  a  naturalist,  exhibited  exceptional  powers  of  defini- 
tion and  description,  while  in  his  philosophical  writings  upon  Evolu- 
tion, his  speculation  far  outran  his  observations,  and  his  theory 
suffered  from  the  absurd  illustrations  which  he  brought  forward  in 

support  of  it His  critics  spread  the  impression  that  he  believed 

animals  acquired  new  organs  simply  by  wishing  for  them.  His  really 
sound  speculation  in  Zoology  was  also  injured  by  his  earlier  thoroughly 
worthless  speculation  in  Chemistry  and  other  branches  of  science. 
Another  marked  defect  was,  that  Lamarck  was  completely  carried 
away  with  the  belief  that  his  theory  of  the  transmission  of  acquired 
characters  was  adequate  to  explain  all  the  phenomena.  He  did  not, 
like  his  contemporaries,  Erasmus  Darwin  and  Goethe,  perceive  and 
point  out,  that  certain  problems  in  the  origin  of  adaptations  were  still 

left  wholly  untouched  and  unsolved His  arguments  are,  in 

most  cases,  not  inductive,  but  deductive,  and  are  frequently  found  not 
to  support  his  law  but  to  postulate  it. 

"It  is  now  a  question  whether  Lamarck's  factor  is  a  factor  in 
Evolution  at  all!  If  it  prove  to  be  no  factor,  Lamarck  will  sink 
gradually  into  obscurity  as  one  great  figure  in  the  history  of  opinion. 
If  it  prove  to  be  a  real  factor,  he  will  rise  into  a  more  eminent  position 
than  he  now  holds, — into  a  rank  not  far  below  Darwin." 

CUVIER   AND    GEOFFROY   ST.   HILAIRE 

Georges  Cuvier  (1769-183 2)  deserves  especial  mention  as  one  of  the 
strongest  negative  factors  in  the  development  of  the  evolution  idea. 
He  was,  first  of  all,  an  opponent  of  Lamarck,  and,  second,  of  evolution 
in  general.  He  ranged  himself  with  Linnaeus  as  a  special  creationist 
and  advocated  the  idea  of  fixity  of  species.  "All  the  beings, "  said  he, 
"belonging  to  one  of  these  forms  (perpetual  since  the  beginning  of  all 
things,  that  is,  the  Creation)  constitute  what  we  call  species."  So 
able  was  Cuvier  and  so  much  in  favor  at  the  French  court  that  he 
succeeded  in  throwing  Lamarck's  views  into  disrepute  and  thus 
greatly  retarded  the  progress  of  evolution.  He  was  brilliant  as  a 
comparative  anatomist  and  palaeontologist  and  will  long  be  known  for 
his  discoveries  in  these  fields. 

E.  Geoff roy  St.  Hilaire  (17 72-1844)  did  his  best  to  defeat  the 
retarding  influence  of  Cuvier.  The  two  engaged  in  a  long  and  bitter 
controversy  over  the  evolution  idea.  While  not  a  supporter  of 
Lamarckism  proper,  he  was  a  thoroughgoing  evolutionist,  favoring 


22         READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

the  doctrine  of  Buffon,  that  the  direct  action  of  the  environment  was 
the  sole  cause  of  evolution.  He  also,  in  a  sense,  anticipated  De  Vries, 
in  that  he  believed  that  new  species  might  be  formed  by  transmutation 
or  sudden  large  variations  occurring  in  one  generation.  "Hence  the 
underlying  causes  of  transformations,"  he  said,  "were  profound 
changes  induced  in  the  egg  by  external  influences,  accidents  as  it  were, 
regulated  by  law. "  The  controversy  between  Cuvier  and  St.  Hilaire 
was  a  losing  one  for  the  latter.  The  cards  were  stacked  against  him 
and  after  him  the  evolution  idea  was  retired  to  comparative  obscurity 
until  revived  by  Charles  Darwin. 

CATASTROPHISM   AND   UNIFORMITARIANISM 

The  development  of  the  science  of  geology  had  a  profound  influence 
upon  that  of  evolution.  The  prevailing  theories  as  to  historical 
geology  during  the  Middle  Ages  involved  the  idea  of  "catastrophism.  " 
According  to  this  view  all  important  changes  in  the  earth's  crust 
represented  sudden  radical  transformations,  involving  earthquakes, 
volcanic  outbursts,  floods,  sudden  upliftings  of  submerged  areas,  or 
equally  sudden  submergence  of  land  bodies.  From  these  ideas  natu- 
rally grew  the  related  idea  of  great,  world-wide  destructions  of  animals 
and  plants,  followed  by  re-creation  of  new  faunas  and  floras.  Cuvier, 
for  example,  interpreted  the  more  or  less  distinct  fossil  strata  as  being 
the  result  of  a  series  of  tremendous  cataclysms,  the  last  of  which  had 
been  the  great  deluge  of  Scripture,  in  which  Noah  figured  prominently. 
He  thought  that  at  each  cataclysm  great  floods  of  water  had  covered 
the  earth,  that  the  existing  animals  had  been  buried  in  mud  and  thus 
preserved  as  fossils,  and  that  a  new  creation  followed  each  cataclysm. 
The  great  strength  of  this  conception  was  that  it  appeared  to  give 
scientific  support  to  both  special  creation  and  the  Mosaic  account  of 
the  "Flood."  As  compared  with  the  pure  evolutionary  conception, 
this  alternative  was  highly  acceptable  to  the  church  and  was  pro- 
claimed as  orthodox.  The  Scotch  philosopher  and  geologist,  Hutton, 
who  lived  during  the  last  half  of  the  eighteenth  century,  combated  the 
idea  of  catastrophism  by  advocating  the  doctrine  of  "uniformitari- 
anism,"  a  view  involving  the  idea  that  past  changes  on  the  earth 
were  the  result  of  the  same  sort  of  gradual  changes  as  are  observed 
to  be  taking  place  today — in  brief,  that  there  has  been  a  strict  uni- 
formity of  change  throughout  the  entire  period  of  geologic  history. 
There  may  have  been,  according  to  this  view,  local  catastrophes, 


HISTORICAL  ACCOUNT  OF  EVOLUTION  THEORY  23 

such  as  volcanic  outbursts,  earthquakes,  and  floods,  but  the  main 
trend  of  change  has  been  slow  and  constant,  due  largely  to  erosion 
and  allied  phenomena.  This  view  had  practically  no  influence 
on  the  ideas  of  the  time  and  for  a  long  period  the  idea  of  catas- 
trophism  triumphed  over  the  more  truly  evolutionary  view  of  uni- 
formitarianism;  thus  the  evolution  idea  was  destined  to  lie  dormant 
till  revived  by  Charles  Darwin. 

THE   REAWAKENING   OF   THE   EVOLUTION   IDEA 

A  number  of  important  influences  paved  the  way  for  the  rehabili- 
tation of  the  evolution  idea  at  the  hands  of  the  younger  Darwin. 
Which  of  these  was  the  most  important  it  is  difficult  to  say.  Prob- 
ably Charles  Lyell's  Principles  of  Geology  and  Malthus'  On  Population 
were  the  most  suggestive  works  that  Darwin  encountered.  He  was 
also  doubtless  influenced  by  Robert  Chambers'  Vestiges  of  Natural 
History  of  Creation  which  appeared  in  1844. 

Charles  Lyell  (i 797-1875)  so  successfully  rehabilitated  the  doctrine 
of  uniformitarianism  in  geology  that  it  became  very  generally  accepted, 
thus  paving  the  way  for  a  more  favorable  consideration  of  the  idea  of 
organic  evolution.  Charles  Darwin  as  a  very  young  man  took  Lyell's 
Principles  of  Geology  with  him  on  his  voyage  on  the  ''  Beagle  "  and  read 
it  with  the  greatest  devotion,  as  is  evidenced  by  his  dedication  of  the 
journal  of  his  voyage:  "To  Charles  Lyell,  Esq.,  F.R.S.,  this  second 
edition  is  dedicated  with  grateful  pleasure,  as  an  acknowledgment 
that  the  chief  part  of  whatever  scientific  merit  this  Journal  and  other 
works  of  the  author  may  possess,  has  been  derived  from  studying  the 
well-known,  admirable  Principles  of  Geology.'' 

Malthus'  influence  on  Darwin's  ideas  is  well  expressed  by  Judd 
as  follows : 

"Fifteen  months  after  this  'systematic  inquiry'  began  [referring 
to  Darwin's  exhaustive  working  over  of  his  notes  taken  during  his 
voyage  on  the  'Beagle'],  Darwin  happened  to  read  the  celebrated 
work  of  Malthus  'On  Population'  for  amusement,  and  this  served  as  a 
spark  falling  on  a  long  prepared  train  of  thought.  The  idea  that  as 
animals  and  plants  multiply  in  geometrical  progression,  while  the 
suppHes  of  food  and  space  to  be  occupied  remain  nearly  constant, 
and  that  this  must  lead  to  a  struggle  for  existence  of  the  most  desperate 
kind,  was  by  no  means  new  to  Darwin,  for  the  elder  De  Candolle, 
Lyell,  and  others  had  enlarged  upon  it;  yet  the  facts  with  regard  to 


24        READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

the  human  race,  so  strikingly  presented  by  Malthus,  brought  the 
whole  question  with  such  vividness  before  him  that  the  idea  of 
'Natural  Selection'  flashed  upon  Darwin's  mind." 

CHARLES   DARWIN    (1809-82) 

Charles  Darwin  is  without  question  the  foremost  figure  in  the 
development  of  the  evolution  idea  and  probably  in  the  development 
of  science  in  general.  The  publication  of  his  book,  The  Origin  of 
Species,  in  1859,  was  the  most  important  event  in  biological  history. 
As  has  been  already  shown,  Darwin's  chief  ideas  had  been  anticipated 
not  by  one  but  by  several  of  his  predecessors.  Nevertheless,  he 
was  the  first  to  furnish  a  really  adequate  proof  of  the  fact  of  evolution 
and  his  causo-mechanical  theory  to  explain  the  method  of  evolution 
was  supported  by  a  mass  of  systematically  arranged  data  such  as  has 
been  paralleled  neither  before  nor  since.  Darwin  was  the  first  evolu- 
tionist effectively  to  employ  the  inductive  method,  that  of  everywhere 
seeking  facts  first  and  then  devising  theories  to  fit  the  facts.  He 
never  allowed  speculation  to  outstrip  observation,  as  nearly  all  of  his 
predecessors  had  done,  but  made  theory  await  the  amassing  of  facts 
in  its  support,  until  the  accumulation  of  the  latter  seemed  almost  to 
speak  out  the  theory  of  themselves.  Our  greatest  debt  to  Darwin  is 
due  to  his  establishment  of  the  factual  basis  of  evolution;  his  selection 
theory  was  relatively  of  minor  significance  in  so  far  as  its  value  in  the 
development  of  the  evolution  idea  was  concerned.  Yet  this  latter 
theory  gained  the  widest  acceptance  among  the  scientifically  inclined 
during  the  entire  post-Darwinian  period.  It  has  been  viciously 
assailed  on  all  sides  and  has  tottered  repeatedly  under  the  attacks 
of  well-trained  adversaries.  Some  of  the  weaker  elements  of  the 
theory  have  given  way  under  stress,  and  the  whole  selection  factor 
as  a  primary  causal  factor  in  evolution  has  been  seriously  called  into 
question;  but  since  Darwin's  time  the  fact  of  evolution  has  been  almost 
universally  accepted. 

The  story  of  Darwin's  life  is  almost  a  romance.  ''  Born  in  1809, " 
says  Lull,'^  ''this  emancipator  of  human  minds  from  the  shackles  of 
slavery  to  tradition  saw  the  light  of  day  upon  the  very  day  that 
ushered  in  the  life  of  Abraham  Lincoln,  the  emancipator  of  human 
bodies  from  a  no  more  real  physical  bondage.  Darwin  studied  first 
at  Edinburgh,  but  finding  medicine  unsuited  to  his  tastes,  entered 
Christ's  College,  Cambridge,  as  a  candidate  for  the  church.    His  love 

'  Richard  Swann  Lull,  Organic  Evolution  (The  Macmillan  Company,  191 7). 


PMOPERTY  LIBRARY 


HISTORICAL  ACCOUNT  OF  EVOLUTION  THEORY  25 

of  Nature,  however,  dominated  all  other  interests  and  shortly  after 
graduation  an  opportunity  came  to  join  the  ship  'Beagle'  as  naturalist 
in  a  voyage  of  exploration  around  the  world.  The  five  years  spent 
upon  this  memorable  journey,  the  narrative  of  which  is  so  admirably 
set  forth  in  the  book,  A  Naturalist's  Voyage  around  the  World,  resulted 
in  the  accumulat  on  of  the  first  of  Darwin's  great  series  of  observations, 
the  final  decision  to  devote  his  life  to  zoological  research,  and  the 
beginning  of  that  illness  which  made  him  a  life-long  invalid.  This 
last  factor  necessitated  a  retired  life  and  thus  proved  of  indirect  bene- 
fit, as  it  enabled  him  to  accomplish  the  immense  amount  of  work 
which  he  did  without  being  impeded  by  the  distractions  of  a  public 
career." 

SUMMARY    OF   DARWIN's    THEORIES 

Since  two  subsequent  chapters  are  to  be  devoted  to  Darwinism, 
only  an  outline  of  Darwin's  theories  need  be  presented  in  the  present 
historical  account. 

Although  Darwin  was  an  all-round  biologist  and  gave  attention 
to  practically  every  phase  of  evolutionary  biology,  he  is  known  espe- 
cially for  his  selection  theories'.  There  are  three  of  these :  the  theory 
of  artificial  selection,  the  theory  of  natural  selection,  and  the  theory  of 
sexual  selection. 

-.  a)  Artificial  selection. — According  to  Darwin  the  commonest 
method  of  producing,  under  human  culture,  new  races  of  animals  and 
plants  is  that  of  selection.  The  breeder  selects  from  among  the  highly 
variable  individuals  of  a  parent-race  those  which  possess  the  begin- 
nings of  desired  modifications,  and  he  breeds  them  together,  expecting 
that  the  offspring  will  show  the  desired  character,  some  in  a  more 
highly  perfected  condition,  others  in  a  less.  The  ones  that  vary 
favorably  are  again  selected  for  breeding  stock,  and  the  same  process 
is  carried  on  until  the  desired  character  has  been  perfected. 

Although  we  now  know  that  this  is  far  from  being  a  typical  experi- 
ence among  breeders,  it  appeared  to  Darwin  to  be  so  typical  that  he 
transferred  the  selection  idea  from  the  breeder  to  Nature,  making 
Nature  the  selecting  agency  responsible  for  the  production  of  natural 
wild  species.     His  argument  is  as  follows: 

b)  Natural  selection. — The  following  factors  are  involved : 
^    I.  All  animals  and  plants  tend  to  multiply  in  geometrical  ratio. 

2.  There  is  not  food  or  room  for  a  much  larger  number  of  animals 
and  plants  than  now  exist. 


26        READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

3.  All  members  of  a  species  vary  in  many  if  not  all  directions. 

4.  Those  that  vary  in  the  more  favorable  directions,  so  as  better 
to  fit  them  to  meet  the  conditions  of  life,  survive  in  larger  numbers  than 
those  varying  in  less  favorable  directions.  This  is  Spencer's  "  survival 
of  the  fittest." 

5.  The  survivors  of  one  generation  become  the  parents  of  the  next 
and,  therefore,  the  more  favorable  characters  are  passed  on  more 
largely  than  the  less  favorable. 

6.  There  is  in  each  generation  a  slow  but  definite  approach  toward 
complete  adaptation  to  life-conditions. 

7.  Variations  neither  useful  nor  harmful  would  not  be  affected  by 
natural  selection,  and  would  be  left  either  as  fluctuating  variations  or 
as  polymorphic  characters. 

c)  Sexual  selection. — This  theory  was  offered  to  supplement  that 
of  natural  selection,  because  Darwin  considered  the  latter  as  inade- 
quate to  explain  the  facts  of  sexual  dimorphism,  or  secondary  sexual 
characters.  The  theory  is  as  follows:  There  is  always  a  contest 
among  males  for  possession  of  females,  in  which  the  inferior  males  are 
eliminated  either  because  they  are,  on  the  one  hand,  less  courageous 
or  weaker  or  less  well  equipped  with  weapons  of  combat,  or  because, 
on  the  other  hand,  the  more  attractive  males,  whether  on  account 
of  colors,  odors,  phosphorescence,  behavior,  etc.,  would  succeed  in 
winning  mates  from  those  less  endowed.  Thus  would  be  enhanced  the 
sexual  dimorphism  until  it  reaches  extremes  in  many  cases  that  are 
truly  remarkable. 

The  name  of  Alfred  Russell  Wallace  (1822-1913)  will  always  be 
associated  with  that  of  Charles  Darwin  as  co-author  of  the  theory  of 
natural  selection.  Wallace  at  the  age  of  twenty-six  went  on  a  natural- 
istic expedition,  primarily  for  collecting  specimens  from  new  regions. 
He  covered  almost  the  same  ground  as  did  Darwin  in  his  voyage 
on  the  ''Beagle."  Wallace  had  read  Lyell's  Principles  of  Geology, 
Malthus'  0«  Population,  Chambers'  Vestiges  of  Creation.  While  in 
Sarawak  he  tells. us:  "I  was  quite  alone  with  one  Malay  boy  as  cook, 
and  during  the  evenings  and  wet  days,  I  had  nothing  to  do  but  to  look 
over  my  books  and  ponder  over  the  problem  which  was  rarely  absent 
from  my  thoughts. "  While  thus  engaged  the  idea  of  natural  selection 
came  to  him  as  though  by  a  sudden  flash  of  insight.  When  the  idea 
was  still  in  process  of  formation  he  wrote  it  out  on  thin  paper  and 
mailed  it  to  Darwin,  stating  that  he  considered  the  idea  new  and 
asking  Darwin  to  show  it  to  Lyell,  who  had  expressed  interest  in  a 


HISTORICAL  ACCOUNT  OF  EVOLUTION  THEORY  27 

former  paper  of  Wallace.  The  ideas  were  expressed  under  the  title 
On  the  Tendency  of  Varieties  to  Depart  Indefiititely  from  the  Original 
Type,  and  it  proved  to  be  an  unusually^ concise  and  lucid  statement  of 
the  main  points  of  the  natural-selection  theory.  Darwin  at  once 
wrote  to  Lyell  as  follows: 

"I  never  saw  a  more  striking  coincidence;  if  Wallace  had  my 
MS  sketch,  written  in  1842,  he  could  not  have  made  a  better  short 
abstract !  Even  his  terms  now  stand  as  heads  of  my  chapters.  Please 
return  to  me  the  MS  which  he  does  not  say  he  wishes  me  to  publish 
but  I  shall,  of  course,  at  once  write  and  offer  to  send  it  to  any  journal. 
So  all  my  originality,  whatever  it  may  amount  to,  will  be  smashed, 
though  my  book,  if  it  ever  have  any  value,  will  not  be  deteriorated, 
as  all  the  labour  consists  in  the  application  of  the  theory.  I  hope  you 
will  approve  of  Wallace's  sketch,  that  I  may  tell  him  what  to  say." 

Lyell  insisted  that  Darwin  publish  an  abstract  of  his  own  work 
simultaneously  with  that  of  Wallace,  and  this  course  was  carried  out. 
Darwin's  generosity  was  equaled  by  that  of  Wallace  who  wrote,  in 
1870: 

"I  have  felt  all  my  life  and  still  feel  the  most  sincere  satisfaction 
that  Mr.  Darwin  had  been  at  work  long  before  me,  and  that  it  was  not 
left  for  me  to  attempt  to  write  The  Origin  of  Species.  I  have  long 
since  measured  my  own  strength  and  know  well  that  it  would  be  quite 
unequal  to  the  task." 

Still  later  he  wrote:  ''I  was  then  (and  often  since)  the  'young 
man  in  a  hurry,'  he  [Darwin]  the  painstaking  student,  seeking  ever 
the  full  demonstration  of  the  truth  he  had  discovered,  rather  than  to 
achieve  immediate  personal  fame." 

One  must  perforce  admit  the  nobility  of  character  of  both  men; 
but  there  can  be  no  serious  competition  between  the  two  for  the  honor 
of  being  called  the  originator  of  the  natural-selection  theory. 

CONTEMPORARY   OPINION   REGARDING   THE   VALIDITY   OF   DARWIN's   VIEWS 

At  first  Darwin  was  inclined  to  believe  that  the  selection  factor 
was  all-sufficient  to  account  for  the  origin  of  species,  as  well  as  that  of 
adaptations;  but  as  time  passed  he  modified  his  earlier  more  sanguine 
views  and  came  to  the  conclusion  "  that  natural  selection  has  been  the 
main  but  not  the  exclusive  means  of  modification."  Many  of  his 
followers  went  to  such  extremes  in  their  advocacy  of  the  all-sufficiency 
of  natural  selection  as  would  not  have  met  with  Darwin's  approval. 


28        READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

"The  first  effect  of  Darwin's  works,"  says  McFarland/  ''was  to 
carry  the  world  of  science  by  storm,  but  at  the  same  time  to  arouse 
intense  hostihty  on  the  part  of  the  theologians  who  found  the  theory 
of  descent  ....  incompatible  with  the  doctrines  of  Creation.  In 
this  conflict  Darwin  took  no  part,  but  was  championed  by  Huxley, 
while  Bishop  Wilberforce  led  the  opposition.  The  battle  was  long 
and  bitter,  there  was  much  acrimonious  writing  on  both  sides,  but 
the  theory  of  descent — the  doctrine  of  evolution — was  found  to  be 
invulnerable  and  at  present  the  theologians  themselves  have  accepted 
it  and  even  make  use  of  it  in  their  own  work. 

"  But  as  the  years  flew  by  the  Darwinian  doctrines  began  to  meet 
with  assaults  from  the  scientists  themselves,  who,  having  endeavored 
to  prove  their  validity,  began  to  find  them  inadequate  to  the  require- 
ments of  expanding  knowledge.  The  question  was  asked,  'What  is 
the  origin  of  the  fittest  ?'  Given  the  fittest,  we  easily  understand  how 
it  is  perpetuated,  but  how  does  it  arise  ?  In  the  striking  phrase  of 
someone:  'Natural  selection  might  explain  the  survival  of  the  fittest 
but  fails  to  account  for  the  arrival  of  the  fittest!' " 

Darwin's  main  supporters  during  the  most  trying  controversial 
period  were  Herbert  Spencer  and  Thomas  H.  Huxley. 

Herbert  Spencer  (i 820-1 903)  was  an  extremely  able  supporter  of 
the  general  theory  of  evolution,  but  was  more  definitely  an  advocate 
of  Lamarckism  than  of  natural  selection.  His  role  was  that  of  a 
champion  of  the  whole  philosophy  of  evolution  as  opposed  to  special 
creation,  and  it  was  largely  due  to  his  forceful  writings  that  Darwinism 
won  the  battle  against  dogmatism.  Spencer  tried  to  explain  the 
structure  of  protoplasm  (living  substance)  on  a  physicochemical 
basis.  He  thought  of  the  structural  units  of  protoplasm  as  compa- 
rable with  the  molecules  of  chemical  compounds,  each  local  region 
of  the  protoplasm  in  the  organism  being  made  up  of  different  kinds  of 
units,  which  he  called  "physiological  units. "  This  conception  of  the 
physical  basis  of  organic  structure  had  a  considerable  influence  in 
shaping  Darwin's  ideas  and  was  probably  the  basis  of  the  latter's 
provisional  theory  of  "pangenesis."  This  theory  was  probably  the 
first  consistently  worked  out  theory  of  the  mechanics  of  heredity. 
It  was  thought  that  every  part  of  the  body  is  continually  giving  off  its 
particular  kind  of  units  ("gemmules")  into  the  blood.  These  gem- 
mules  are  transported  by  the  blood  stream  to  all  parts  of  the  body  and 

^  J.  McFarland,  Biology,  General  and  Medical  (The  Macmillan  Company, 
1918). 


HISTORIC.\L  ACCOUNT  OF  EVOLUTION  THEORY  29 

collect  in  the  germ  cells.  This  was  supposed  to  account  for  the  fact 
that  from  the  germ  cell  will  develop  an  organism  like  the  parent  in 
various  details.  If  a  part  of  the  body  was  modified  through  func- 
tioning or  through  changed  environment,  it  would  have  modified 
gemmules,  which,  in  turn,  would  go  to  the  germ  cells  and  carry  over 
the  modification  to  the  next  generation.  This  theory  was  not  satis- 
factory even  to  Darwin  and  is  now  only  of  historical  interest. 

Spencer  is  best  known  in  the  history  of  the  evolution  theory  as  an 
ardent  neo-Lamarckian.  He  states  his  belief  as  follows:  '^  Change  of 
function  produces  change  of  structure;  it  is  a  tenable  hypothesis  that 
changes  of  structure  so  produced  are  inherited. "  This  idea  prevailed 
until  it  was  cast  down  by  Weismann. 

Thomas  Henry  Huxley  (1825-95),  ^^^  of  the  keenest,  most  analyti- 
cal thinkers  of  the  nineteenth  century,  not  only  defended  the  general 
doctrine  of  evolution  against  Bishop  Wilberforce  and  his  aids,  but  was 
an  able  investigator  in  the  fields  of  comparative  anatomy  and  embry- 
ology. "At  the  British  Association  at  Oxford  in  i860,"  says  Judd, 
''after  an  American  professor  had  indignantly  asked  'Are  we  a 
fortuitous  concourse  of  atoms?'  as  a  comment  on  Darwin's  views, 
Dr.  Samuel  Wilberforce,  the  Bishop  of  Oxford,  ended  a  clever  but 
flippant  attack  on  the  Origin  by  enquiring  of  Huxley,  who  was  present 
as  Darwin's  champion,  if  it  'was  through  his  grandfather  or  his  grand- 
mother that  he  claimed  his  descent  from  a  monkey  ? ' 

"Huxley  made  the  famous  and  well-deserved  retort :  'I  asserted — 
and  I  repeat — that  a  man  has  no  reason  to  be  ashamed  of  having  an 
ape  for  his  grandfather.  If  there  were  an  ancestor  whom  I  should 
feel  ashamed  of  recalling,  it  would  rather  be  a  man — a  man  of  restless 
and  versatile  intellect — who  not  content  with  success  in  his  own  sphere 
of  activity,  plunges  into  scientific  questions  with  which  he  has  no  real 
acquaintance,  only  to  obscure  them  by  aimless  rhetoric,  and  distract 
the  attention  of  his  hearers  from  the  real  point  at  issue  by  eloquent 
digressions  and  skilled  appeals  to  religious  prejudice!' 

"Huxley  himself  accepted  the  theory  of  Natural  Selection — but 
not  without  some  important  reservations — these,  however,  did  not 
prevent  him  from  becoming  its  most  ardent  and  successful  champion. 
Darwin  used  to  acknowledge  Huxley's  great  service  to  him  in  under- 
taking the  defense  of  the  theory — a  defense  which  his  own  hatred  of 
controversy  and  state  of  health  made  him  unwilling  to  undertake — 
by  laughingly  calling  him  'my  general  agent'  while  Huxley  himself  in 
replying  to  the  critics,  declared  he  was  'Darwin's  bulldog.'" 


30        READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

Ernst  Haeckel  (1834-1919)  was  one  of  the  earliest  and  most 
influential  followers  of  Darwin  in  Germany.  In  his  Generelle  Mor- 
phologie,  published  in  1866,  seven  years  after  the  Origin  of  Species 
first  appeared,  he  applied  the  doctrine  of  evolution,  and  especially 
the  theory  of  natural  selection,  to  the  whole  field  of  vertebrate  mor- 
phology. Beyond  question  Haeckel  overapplied  the  theory  and  in  a 
sense  weakened  its  influence  by  his  rather  uncritical  use  of  materials. 
His  writings  have  been  translated  into  most  languages  and  ''are 
popularly  believed  to  represent  the  best  scientific  thought  on  the 
matter. "  Biologists  today,  however,  are  apt  to  look  askance  at 
Haeckel's  works  and  to  consider  that  they  did  more  harm  than  good 
to  Darwinism. 

August  Weismann  (1834-1914)  was  the  first  really  original 
evolutionist  after  Darwin.  Like  other  thinkers  of  his  time,  he  realized 
that  further  progress  in  the  knowledge  of  the  causal  basis  of  evolution 
lay  in  further  investigation  of  the  causes  of  variation  and  the  physical 
basis  of  heredity.  Weismann  has  been  classed  as  a  neo-Darwinian 
because  he  was  a  strong  advocate  of  some  form  of  selection,  but  his 
"selection"  was  not  the  selection  of  Darwin.  Realizing  that  the 
greatest  weakness  of  the  natural-selection  theory  lay  in  its  inadequacy 
as  an  originator  of  variations,  he  proposed  the  "germinal-selection" 
theory.  He  contended  that  all  heritable  variations  have  their  origin 
in  the  germ  cell,  and  therefore  that  a  new  type  of  organism  arises  only 
from  a  changed  type  of  germ  cell.  The  germinal-selection  theory 
stands  out  in  striking  contrast  with  Darwin's  "pangenesis"  theory. 
The  former  is  centrifugal,  the  latter  centripetal.  "Determiners"  of 
new  characters,  according  to  Weismann,  arise  in  the  germ  plasm  and 
work  outward  to  all  parts  of  the  developing  body;  while  the  "gem- 
mules,"  Darwin's  equivalent  of  determiners,  originate  in  the  body 
tissues  and  are  carried  to  the  germ  cells  in  each  generation.  Accord- 
ing to  Weismann,  there  is  a  struggle  among  the  determiners  for  the 
available  food  and  favorable  positions  in  the  germ  cell,  and  those  that 
receive  the  most  food  and  the  best  positions  gain  an  initial  advantage, 
so  that  they  are  able  to  initiate  the  development  of  larger  or  more 
perfectly  adapted  organs.  The  descendants  through  cell  division  of 
these  favored  determiners  are  in  a  position  to  compete  with  other 
determiners  on  a  more  favorable  footing  in  each  succeeding  generation, 
so  that  the  character  represented  by  them  steadily  increases  in  a  linear 
or  definitely  directed  fashion  until  it  reaches  the  state  of  complete 
adaptation  or  fitness.  Such  a  character  may  even  continue  its  direct 
line  of  advance  beyond  the  point  of  maximum  fitness  and  result  in 


HISTORICAL  ACCOUNT  OF  EVOLUTION  THEORY  31 

what  are  known  as  overspecializations.  The  theory  therefore  would, 
if  well  founded,  account  not  only  for  the  initial  stages  of  new  adaptive 
characters,  but  also  for  overspecializations,  two  phenomena  that 
natural  selection  was  unable  to  account  for.  Not  only  were  pro- 
gressive evolutionary  changes  explained  by  germinal  selection,  but 
regressive  changes  seemed  to  be  .even  more  readily  accounted  for  on 
this  basis.  In  the  struggle  among  determiners  in  the  germ  cell 
some  of  the  less  favored  units  would  be  handicapped  at  the  outset  by 
insufficient  food  or  unfavorable  position  and  would  produce  smaller  or 
less  effective  structures.  Progressively,  from  generation  to  generation, 
these  weakened  determiners  would  lose  ground  and  become  less  and 
less  successful  in  competition  until  they  were  weaklings  among 
determiners  and  would  be  able  to  initiate  only  degenerate  or  vestigial 
structures,  or  else  would  die  out  and  lose  their  place  altogether,  thus 
accounting  for  total  losses  of  structure. 

This  theory  does  not  exclude  natural  selection,  but  rather  increases 
its  importance,  for  every  structure  that  arises  to  the  threshold  of 
utility  or  disutility  meets  the  winnowing  process  of  natural  selection. 
The  fitter  individuals  survive  in  the  long  run  and  these  perpetuate  the 
germ  cells  in  which  the  successful  determiners  reside. 

A  slightly  different  explanation  of  degenerating  structures  in- 
volves the  principle  of  ''panmixia. "  According  to  this  idea,  changing 
environmental  conditions  may  render  certain  adaptive  organs  of 
lessened  value  or  of  no  value,  as  would  be  the  case  in  the  eyes  of  cave 
animals.  In  different  individuals  the  eye  determiners  would  vary  in 
their  success  in  competition  with  other  determiners,  and  since  natural 
selection  would  no  longer  put  a  premium  on  perfect  eyes,  all  grades  of 
eyes  would  be  equally  inherited  and  gradually  the  poorer  or  degenerate 
eyes  would  become  more  numerous,  till,  finally,  there  would  be  no 
good  eyes  in  the  race.  Thus  it  will  be  seen  that  the  germinal-selection 
theory  was  auxiliary  to  natural  selection  and  tended  to  support  the 
latter  at  two  of  its  weakest  points.  But  the  supporting  theory  itself 
has  the  fundamental  weakness  of  lacking  a  factual  basis.  It  is  purely 
hypothetical  and  cannot  be  put  to  an  experimental  test.  Every 
time  an  objection  to  the  theory  was  raised  an  auxiliary  h>T)othesis 
was  added  to  explain  away  the  difficulty,  till  finally  it  fell  to  the  ground 
through  sheer  top-heaviness,  unable  further  to  support  its  intricate 
structure  of  interrelated  hypotheses. 

A  much  more  valuable  and  lasting  contribution  of  Weismann  was 
his  theory  of  "germinal  continuity"  and  of  the  ''apartness  of  the  germ 
plasm. "     The  whole  theory  has  come  to  be  known  as  the  "  germ-plasm 


32         READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

theory,"  which  forms  the  framework  of  nearly  all  of  our  modern 
genetics.  According  to  this  view  the  germ  plasm  is  immortal  in 
that  it  is  perpetuated  from  generation  to  generation  through  the 
instrumentality  of  mitotic  cell  division,  each  germ  cell  being  the  prod- 
uct of  the  division  of  a  previous  germ  cell  back  to  the  first  germ  cell 
that  arose  at  the  dawn  of  life.  Thus  a  germ  cell  cannot  be  a  product 
of  the  soma,  but  the  soma  is  the  product  of  germ  cells.  The  soma  loses 
its  generalized  characters  and  specializes  in  various  ways.  Once 
specialized,  soma  cells  are  believed  to  have  lost  their  capacity  to  play 
a  germinal  role.  Specialization  means  mortality.  Thus  the  relation- 
ship between  parent  and  offspring  is  not  that  the  parent  gives  rise  to 
the  offspring,  but  that  the  same  germ  plasm  gives  rise  to  both  parent 
and  offspring. 

The  logical  conclusion  to  which  this  line  of  reasoning  leads  is  that 
the  changes  in  the  soma,  no  matter  how  produced,  are  helpless  to 
produce  any  effect  upon  the  germ  plasm,  since  germ  cells  come  only 
from  germ  cells  and  not  from  soma  cells.  Consequently  Weismann 
led  the  assault  against  Lamarckism  and  won  the  day  so  conclusively 
that  even  in  these  modern  times  few  biologists  have  the  temerity  to 
express  aloud  any  definite  belief  in  the  inheritance  of  acquired  charac- 
ters. Weismann's  germ-plasm  idea  is  the  cornerstone  of  modern 
genetics,  though  there  are  some  forward-looking  biologists  who,  looking 
at  things  with  a  physiological  bias,  cannot  make  themselves  believe  in 
the  total  independence  of  any  tissue — even  the  sacred  germ  plasm. 

Weismann's  influence  was  very  great,  especially  during  the  last 
decade  of  the  nineteenth  century,  and  his  theories  gave  rise  to  an 
immense  amount  of  research,  chiefly  of  a  cytological  and  embryo- 
logical  character. 

ISOLATION   THEORIES 

Among  the  theories  subsidiary  to  natural  selection  as  an  aid  to 
species  forming  are  the  various  isolation  theories.  One  of  the  weak- 
nesses inherent  in  natural  selection  had  to  do  with  the  probable 
swamping  out  of  new  types  by  promiscuous  breeding  with  the  more 
numerous  individuals  of  the  older  types.  "Anything,"  says  Metcalf, 
''which  divides  a  species  into  groups,  which  do  not  freely  interbreed, 
is  said  to  segregate  (isolate)  the  members  of  the  species  into  these  sub- 
divisions." 

Some  American  writers,  especially  Jordan  and  Kellogg,  Gulick,  and 
Crampton,  have  dealt  with  the  isolation  factor  in  evolution  and  believe 


HISTORICAL  ACCOUNT  OF  EVOLUTION  THEORY  33 

that  it  is  a  major  factor  of  as  great  importance  in  species  forming,  or 
nearly  so,  as  natural  selection.  But  the  prevailing  opinion  seems  to  be 
that  isolation  is  really  a  kind  of  selection,  more  like  artificial  selection 
than  anything  else,  which  separates  out  certain  pure  lines  and  prevents 
promiscuous  interbreeding.  Various  agents  are  known  to  produce 
isolation  by  erecting  barriers  to  interbreeding  between  groups  of 
individuals  within  a  species.  These  segregative  factors  may  be 
geographical,  climatic,  reproductive,  physiological,  or,  in  plants,  the 
result  of  soil  diversity.  Thus  a  mountain  range,  on  the  two  sides  of 
which  a  species  migrates,  effectively  separates  the  species  into  two 
independent  groups.  Heat,  cold,  moisture,  etc.,  separate  others. 
Reproductive  incompatibility  between  new  and  older  types  is  equally 
effective,  as  is  assortative  mating  of  like  with  like.  Like  natural  selec- 
tion, isolation  has  nothing  to  do  with  the  origin  of  new  types,  but 
merely  aids  in  the  preservation  of  types  when  once  formed.  Were 
there  not  spontaneous  variations  among  animals  and  plants,  there 
would  be  nothing  to  isolate.  Therefore  isolation  plays  only  an 
auxiliary  role,  helping  to  preserve  new  races  once  they  are  formed. 

ORTHOGENESIS   THEORIES 

''The  orthogenetic  evolution  theories  of  various  authors,  based 
upon  the  assumed  occurrence  of  variations  in  determinate  lines  or 
directions  (a  restricted  and  determinate  variation  as  compared  with 
the  nearly  infinite,  fortuitous,  and  indeterminate  variation  assumed 
in  the  selection  theories),  are  of  several  types.  The  mention  of  two 
will  reveal  pretty  well  the  more  important  characters  of  all.  Not  a 
few  biologists  have  always  believed  in  the  existence  of  a  sort  of  mystic, 
special  vitalistic  force  or  principle  by  virtue  of  which  determination 
and  general  progress  in  evolution  is  chiefly  fixed.  Such  a  capacity, 
inherent  in  living  matter,  seems  to  include  at  once  possibility  of  pro- 
gressive or  truly  evolutionary  change.  Not  all  evolution  is  in  a  single 
direct  line,  to  be  sure;  ascent  is  not  up  a  single  ladder  or  along  a  single 
geological  branch,  but  these  branches  are  few  (as  indeed  we  actually 
know  them  to  be,  however  the  restriction  may  be  brought  about) 
and  the  evolution  is  always  progressive,  that  is,  toward  what  we, 
from  an  anthropocentric  point  of  view,  are  constrained  to  call  higher 
and  higher  or  more  ideal  Hfe  stages  and  conditions. 

"Other  naturalists  also  seeming  to  see  this  source  of  determinate 
or  orthogenetic  evolution,  but  not  inclined  to  surrender  their  dis- 
belief in  vitalism,  in  forces  over  and  beyond  the  familiar  ones  of  the 


34        READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

physicochemical  world,  have  tried  to  adduce  a  definite  causomechani- 
cal  explanation  of  orthogenesis.  The  best  and  most  comprehensive 
types  of  this  explanation  are  those  essentially  Lamarckian  in  principle, 
in  which  the  direct  influence  of  environmental  conditions,  the  direct 
reactions  of  the  life  stuff  to  stimuli  and  influences  from  the  world 
outside,  are  the  causal  factors  in  such  an  explanation.  But  while 
every  naturalist  will  grant  that  such  factors  do  change  and  control 
in  a  considerable  degree  the  life  of  the  individual,  most  see  no  mechan- 
ism or  means  of  extending  this  control  directly  to  the  species." 

The  above-quoted  paragraphs  from  Jordan  and  Kellogg^  will 
serve  to  place  before  the  reader  the  general  ideas  involved  in  the 
orthogenesis  conception.  A  brief  account  of  the  various  special 
theories  of  orthogenesis  follows: 

Carl  von  NdgeWs  ideas  of  orthogenesis  involve  a  belief  in  a  sort  of 
mystical  principle  of  progressive  development,  a  something,  quite 
intangible,  that  exists  in  organic  nature,  which  causes  each  organism, 
to  strive  for  or  at  least  make  for  specialization  or  perfect  adaptation. 
This  idea  of  an  inner  driving  and  directing  force  reminds  one  of  the 
"entelechy"  of  Driesch,  or  Bergson's  '^  creative  evolution."  Nageli 
believed  that  animals  and  plants  would  have  developed  essentially 
as  they  have  without  any  struggle  for  existence  or  natural  selection. 
This  form  of  orthogenesis  theory,  then,  is  alternative  to  natural 
selection. 

Theodore  Ewicr''s  theory  of  orthogenesis  is  more  scientific  and  less 
mystical  than  Nageli's.  He  believed  that  lines  of  evolution  were  not 
miscellaneous  and  haphazard,  but  were  confined  to  a  few  definite 
directions,  determined  at  their  initial  stages  not  by  natural  selection 
but  by  the  laws  of  organic  growth,  aided  by  the  inheritance  of  acquired 
characters.  A  new  character  makes  a  beginning  as  would  the  first 
step  in  a  slow  chemical  change,  or  series  of  such  changes,  and  it  must 
go  through  to  a  fixed  end,  under  given  conditions,  just  as  surely  as  does 
the  chemical  process.  Only  when  a  given  character  or  line  of  evolu- 
tion results  in  the  production  of  a  ver>'  positive  advantage  or  dis- 
advantage to  the  species  does  natural  selection  step  in  to  interfere 
with  orthogenesis.  The  causes  of  orthogenesis  are  said  "to  lie  in  the 
effects  of  external  influences,  climate,  nutrition,  or  the  given  constitu- 
tion of  the  organism." 

Actual  species-forming,  or  the  breaking-up  into  specific  units  of- 
the  orthogenetic  lines  of  change,  depends,  according  to  Eimer,  upon 

^  Jordan  and  Kellogg,  Evolution  and  Animal  Life  (D.  Appleton  and  Company). 


HISTORICAL  ACCOUNT  OF  EVOLUTION  THEORY  35 

three  factors:  a  standstill  or  cessation  of  development  on  the  part  of 
some  lines;  sudden  development  by  leaps  (practically  mutations); 
and  hindrance  or  difficulty  of  reproduction  (the  type  of  thing  that 
Romanes  emphasized  as  physiological  isolation  ten  years  later). 
Eimer  illustrated  his  theories  by  the  evolution  of  color  patterns  in 
lizards  and  those  on  the  wings  of  butterflies.  In  both  he  believed  that 
longitudinal  stripes  were  primitive,  that  rows  of  dots  followed  these 
which  were  in  turn  followed  by  crossbands,  reticular  patterns,  and 
finally  by  solid  coloration.  This  hypothetical  phylogenetic  order  is 
more  or  less  closely  paralleled  by  the  ontogenetic  order,  in  the 
lizards  at  least. 

It  will  be  noted  that  Elmer's  theory  places  natural  selection  in  a 
subordinate  position,  but  does  not  dismiss  it  altogether,  as  is  done  by 
Nageli.  It  aids  natural  selection  in  explaining  adaptations  in  that  it 
furnishes  for  natural  selection  various  characters  of  selective  value, 
which  may  be  either  perpetuated  or  eliminated  according  to  their 
utility. 

E.  D.  Cope,  a  leading  American  palaeontologist  of  the  past  cen- 
tury, had  an  orthogenetic  theory  involving  his  ideas  of  "bathmism" 
(growth  force),  ''kinetogenesis"  (direct  effect  of  use  and  disuse  and 
environmental  influence),  and  ''archaesthetism"  (influence  of  primi- 
tive consciousness).  It  may  be  said  that  his  ideas  were  Lamarckian 
throughout.  In  common  with  the  majority  of  palaeontologists  of 
later  date — Osboj-n,  WiUiston,  Hyatt,  Smith,  and  others — Cope  felt 
the  need  of  some  factor  other  than  natural  selection  to  explain  the 
apparent  steady  progress  of  characters  in  definitely  directed  lines  as 
seen  in  the  fossils.  It  is  natural  therefore  that  palaeontologists  almost 
universally  lay  hold  of  both  Lamarckian  and  orthogenesis  ideas. 

Charles  Otis  Whitman,  who,  until  his  death  over  ten  years  ago,  was 
considered  the  leading  American  zoologist,  had  strong  leanings  toward 
orthogenesis.     In  one  of  his  few  publications  he  says: 

"Natural  selection,  orthogenesis,  and  mutation  appear  to  present 
fundamental  contradictions;  but  I  believe  that  each  stands  for  truth, 
and  reconciHation  is  not  far  distant.  The  so-called  mutations  of 
Oenothera  are  indubitable  facts;  but  two  leading  questions  remain  to 
be  answered.  First,  are  these  mutations  now  appearing,  as  is  agreed, 
independently  of  variation,  nevertheless  the  products  of  variations  th^ 
took  place  at  an  earlier  period  in  the  history  of  these  plants  ?  Secondly, 
if  species  can  spring  into  existence  at  a  single  leap,  without  the  assist-  , 
ance  of  cumulative  variations,  may  they  not  also  originate  with  such 


36        READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

assistance  ?  That  variation  does  issue  a  new  species,  and  that  natural 
selection  is  a  factor,  though  not  the  only  factor,  in  determining  results, 
is,  in  my  opinion,  as  certain  as  that  grass  grows  although  we  cannot 
see  it  grow.  Furthermore,  I  believe  I  have  found  indubitable  evidence 
of  species-forming  variation  advancing  in  a  definite  direction  (ortho- 
genesis), and  likewise  of  variations  in  various  directions  (amphi- 
genesis).  If  I  am  not  mistaken  in  this,  the  reconciliation  for  natural 
selection,  and  orthogenesis  is  at  hand." 

In  concluding  this  brief  account  of  orthogenesis,  it  should  be  said 
that  definitely  directed  evolution  is  now  believed  to  be  one  of  the  laws 
of  organic  evolution,  but  that  we  have  no  clear  ideas  as  yet  as  to  what 
are  its  underlying  causes.  Therefore  orthogenesis  is  not  a  causo- 
mechanical  theory  of  evolution  at  all. 

MUTATION   OR  HETEROGENESIS   THEORIES 

The  theory  of  "mutations"  is  associated  with  the  name  of  Hugo 
De  Vries,  the  well-known  Dutch  botanist;  that  of  "heterogenesis," 
with  the  name  of  H.  Korchinsky,  a  Russian. 

Though  Korchinsky  anticipated  De  Vries  by  several  years,  his 
work  was  not  supported  by  the  large  amount  of  experimental  data 
that  characterized  that  of  the  great  Dutch  worker.  The  relative 
claims  for  recognition  as  the  founder  of  the  mutation  theory  are 
almost  on  a  par  with  those  of  Darwin  and  Wallace  for  the  natural- 
selection  theory.  Both  Darwin  and  De  Vries  held  .back  their  theo- 
ries until  they  appeared  to  be  adequately  supported  by  personally 
collected  facts. 

There  is  a  striking  parallelism  between  the  ideas  and  conclusions 
of  De  Vries  and  those  of  Korchinsky,  and  since  this  is  true  a  resume  of 
De  Vries's  better-known  work  will  serve  to  give  the  essentials  of  the 
whole  conception. 

De  Vries  began  his  genetic  experiments  by  a  study  of  the  variations 
of  plants  in  the  field.  After  learning  their  normal  variability  in 
nature,  he  transferred  them  to  the  experimental  garden  and  there 
attempted  to  improve  them  by  selection.  He  found  that  the  improved 
living  conditions  due  to  better  soil  and  cultivation  induced  a  wider 
range  of  variability  in  size,  luxuriance,  and  fecundity.  Such  variations 
were  plus  or  minus  in  their  character,  fluctuating  about  a  mean  or 
average.  It  was  exactly  this  type  of  variability  that  Darwin  empha- 
sized as  the  raw  material  of  evolution;  but  De  Vries  found  by  experi- 
ment that  selection  had  no  permanent  hereditary  effect  when  based 


HISTORICAL  ACCOUNT  OF  EVOLUTION  THEORY  37 

to  fluctuating  variations,  since  the  latter  were  merely  somatic  responses 
on  variable  growth  conditions.  This  negative  finding  led  him  to 
renewed  interest  in  discontinuous  or  saltatory  variations  as  the  only 
alternative  to  fluctuating  or  continuous  variations. 

He  looked  far  and  wide  among  species  of  wild  plants  for  a  species 
that  might  exhibit  a  significant  amount  of  saltatory  variation  and 
finally  discovered  in  the  evening  primrose  {Oenothera  lamarckiana) 
what  seemed  to  exhibit  exactly  the  hoped-for  characteristics.  This 
large,  stately  plant  with  conspicuous  yellow  blooms  had  escaped  from 
cultivation  and  was  growing  wild  in  the  fields.  In  addition  to  a  large 
number  of  plants  that  showed  only  minor  differences  among  them- 
selves, De  Vries  found  several  individuals  growing  among  the  typical 
individuals  which  differed  not  merely  in  degree  but  in  kind.  These 
were  as  different  as  distinct  varieties,  and,  when  the  seeds  were 
planted  in  the  garden  they  bred  true  to  their  kind.  The  only  ques- 
tion now  was  whether  they  had  actually  arisen  from  typical  parents. 
To  test  this  possibility,  seeds  of  several  typical  plants  were  planted 
in  the  garden;  the  result  being  not  only  a  repetition  of  the  pecuHar 
types  observed  in  the  field,  but  of  about  a  dozen  other  true  breed- 
ing types  with  well-marked  differences  from  the  parent-species  and 
among  themselves. 

These  new  types  De  Vries  considered  as  new  elementary  species 
and  he  called  them  "mutants."  They  came  into  existence  suddenly 
in  one  generation  and,  as  a  rule,  bred  true.  Whatever  factors  were 
responsible  for  mutations,  the  seat  of  origin  must  have  been  in  the 
germ  cell  and  not  in  the  soma.  Consequently  they  were  inherited 
fully  from  the  start.  The  same  mutations  occurred  in  considerable 
numbers  and  in  successive  years.  In  one  case  a  given  mutation 
occurred  only  once  in  eight  years  of  observation.  Some  mutants 
were  robust  and  successful,  others  were  weak  and  incapable  of  living 
under  natural  conditions,  others  were  sterile.  On  the  basis  of  these 
results,  which  are  reported  in  detail  in  chapter  xxiv,  De  Vries  came 
to  the  conclusion  that  evolution  was  based  upon  the  sudden  appear- 
ance of  new  varieties  or  elenientary  species  and  not  upon  the  natural 
selection  of  fluctuating  variations. 

The  mutation  theory  compared  and  contrasted  with  the  natural 
selection  theory. — It  will  be  recalled  that  the  raw  material  upon  which 
natural  selection  works  is  the  minute  individual  or  continuous  varia- 
tion that  is  universal  in  all  living  forms  and  is  known  to  be  largely 
somatic  in  character  and  due  to  differences  in  environment.     Darwin 


SS        READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

did  not  distinguish  between  somatic  and  germinal  variations.  The 
essential  feature  of  mutations  is  that  they  are  germinal  in  origin  and 
therefore  come  forth  full-fledged  in  the  first  generation  arising  from 
the  changed  germ.  Darwin  recognized  '^saltatory  variations"  or 
''sports/'  which  are  mutations,  but  did  not  consider  them  of  suffi- 
ciently frequent  occurrence  to  furnish  an  adequate  material  for 
selection. 

De  Vries,  on  his  side,  did  not  discard  the  principle  of  selection, 
but  showed  that  selection  acted  as  between  mutants,  serving  to  elimi- 
nate those  which  are  unfit  and  allowing  the  sufficiently  fit  to  survive 
alongside  the  parent-types.  According  to  Darwin's  view,  the  new 
t\^es  arose  only  at  the  expense  of  the  old,  for  only  through  the  elimina- 
tion of  the  old  (less  fit)  types  could  the  new  types  progress  toward 
further  fitness.  Darwin's  view  was  ill  suited  to  explain  the  origin  of 
new  distinct  types,  because  the  process  of  selection  proceeded  by 
imperceptible  steps.  De  Vries's  view  gives  us  distinctly  different, 
pure  breeding  types  at  once  that,  if  isolated,  would  be  new  elementary 
species  from  the  first. 

In  conclusion  it  may  be  said  that  the  mutation  theory  was  at 
first  intended  as  a  substitute  for  natural  selection,  but  that  later  the 
selection  idea  was  adopted  as  a  directive  principle,  guiding  mutations 
toward  adaptiveness. 

THE   RISE   AND   VOGUE    OF   BIOMETRY 

No  historical  account  of  the  development  of  the  evolution  idea 
would  be  complete  without  a  statement  of  the  role  played  by  biometry 
in  the  study  of  evolutionary  data.  Biometry  is  the  statistical  study 
of  variation  and  heredity.  During  the  last  decade  of  the  nineteenth 
century  it  became  obvious  to  those  who  had  followed  the  progress 
of  the  subject  that  farther  advance  toward  the  solution  of  the 
problem  of  the  causes  of  evolution  must  come  from  a  better  under- 
standing of  variation  and  heredity,  the  two  fundamental  factors 
involved.  Three  main  modes  of  attack  were  developed  during  these 
years:  the  statistical  (biometry),  the  experimental  (chiefly  breeding 
work),  and  the  microscopical  (cytology  or  the  study  of  the  minute 
structure  of  the  germ  cells). 

Sir  Francis  Gallon,  a  cousin  of  Charles  Darwin,  was  the  founder 
of  biometry.  He  applied  certain  already  understood  principles  that 
had  been  developed  mainly  in  the  study  of  the  laws  of  chance  to  the 
study  of  variations,  and,  by  comparing  the  boiled-down  formulas 


HISTORICAL  ACCOUNT  OF  EVOLUTION  THEORY  39 

resulting  from  his  computations  of  parental  generations  with  those  of 
offspring,  he  arrived  at  two  laws  of  heredity:  the  law  of  filial  regres- 
sion, and  that  of  ancestral  shares  of  inheritance.  The  essence  of  the 
first  was  that  the  offspring  of  exceptional  parents  tend  to  regress 
toward  mediocrity  in  proportion  to  the  degree  of  parental  excep- 
tionalness.  The  second  law  was  really  explanatory  of  the  first,  for  it 
was  found  that  the  offspring  inherit  not  only  from  parents,  but  from 
the  various  grades  of  ancestors,  and  it  was  the  pulldown  of  a  miscel- 
laneous ancestry  that  made  for  regression  toward  mediocrity.  It 
appeared  that  half  of  the  hereditary  influence  could  be  assigned  to 
parents,  half  of  the  remainder  to  grandparents,  half  of  the  remaining 
remainder  to  great-grandparents,  and  so  on  down  the  line. 

Karl  Pearson,  a  pupil  and  follower  of  Galton,  has  carried  the  study 
of  biometry  to  a  more  highly  refined  state.  His  attempt  has  been  to 
apply  to  the  study  of  evolution  the  precise  quantitative  methods  which 
are  used  in  physics  and  in  chemistry.  While  much  of  Pearson's  work  is 
far  beyond  the  range  of  the  average  professional  biologist  today,  it 
is  extremely  useful  as  a  tool  in  handling  data  in  which  great  accuracy 
is  demanded.  Frequently,  however,  the  methods  are  far  too  refined 
for  the  material,  and  much  time  is  wasted  in  handling  crude  data 
by  means  of  highly  refined  instruments  of  measurement  and  ultra- 
accurate  mathematical  methods. 

On  the  whole  the  contributions  of  biometry  to  our  understanding 
of  the  causes  of  evolution  are  rather  disappointing.  About  the  only 
clean-cut  finding  has  been  the  discovery  that  some  variations  are 
continuous  and  others  discontinuous.  The  former  are  capable  of  being 
expressed  in  a  single  curve  with  a  single  mode,  while  the  latter  are 
expressed  in  bimodal  or  polymodal  curves.  If  material  is  homo- 
geneous to  start  with  it  is  likely  to  give  monomodal  curves,  but  if  it  is 
heterogeneous,  its  heterogeneity  will  be  revealed  by  the  plural  modes. 
In  a  subsequent  connection  (chapter  xxv)  some  further  account  of  the 
details  of  biometry  will  be  presented.  We  must  for  the  present  be 
content  with  having  placed  biometry  in  its  setting  as  one  step  in  the 
advance  of  the  evolution  idea. 

MODERN  EXPERIMENTAL  EVOLUTION 

''While  De  Vries,"  says  Castle,^  ''was  engaged  in  his  studies  of  the 
evening  primrose  he  hit  upon  an  idea  far  more  important,  as  most 
biologists  now  believe,  than  the  idea  of  mutation,  though  De  Vries 

^  W.  E,  Castle,  Genetics  and  Eugenics  (Harvard  University  Press,  1920),  p.  82. 


40        READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

himself,  both  before  and  since,  has  seemed  to  regard  it  as  of  minor 
importance.  He  called  this  the  Haw  of  splitting  of  hybrids.^  The  same 
law,  it  is  claimed,  was  independently  discovered  about  the  same  time 
by  two  other  botanists,  Correns  in  Germany,  and  Tschermak  in 
Austria.  Further,  historical  investigations  made  by  De  Vries  showed 
that  the  same  law  had  been  discovered  and  clearly  stated  many  years 
previously  by  an  obscure  naturalist  of  Briinn,  Austria,  named  Gregor 
Mendel,  and  we  have  now  come  to  call  this  law  by  his  name,  MendeVs 
Law.  ^lendel  was  so  little  known  .when  his  discovery  was  published 
that  it  attracted  little  attention  from  scientists  and  was  soon  forgotten, 
only  to  be  unearthed  and  duly  honored  years  after  the  death  of  its 
author.  Had  Mendel  lived  forty  years  later  than  he  did,  he  would 
doubtless  have  been  a  devotee  of  biometry,  for  he  had  a  mathematical 
type  of  mind  and  his  discovery  of  a  law  of  hybridization  was  due  to  the 
fact  that  he  applied  to  his  biological  studies  methods  of  numerical 
exactness  which  he  had  learned  from  algebra  and  physics.  In  biology 
he  was  an  amateur,  being  a  teacher  of  the  physical  and  natural  sciences 
in  a  monastic  school  at  Briinn.  Later  he  became  head  of  the 
monastery  and  gave  up  scientific  work,  partly  because  of  other  duties, 
partly  because  of  failing  eyesight." 

There  had  been  plant-hybridizers  before  Mendel,  but  their  lack 
of  exactness  in  technique  had  prevented  them  from  discovering  the 
law  of  segregation  or  splitting  of  hybrids. 

Joseph  Gottlieb  Kolrenter  (1783-1806),  who  really  belonged  to  the 
period  of  Lamarck,  barely  missed  making  the  discovery  that  was 
afterward  made  by  Mendel.  The  salient  features  of  his  work  are 
according  to  Castle:^ 

"  I.  Kolreuter  established  the  occurrence  of  sexual  reproduction  in 
plants  by  showing  that  hybrid  offspring  inherit  equally  from  the 
pollen  plant  and  the  seed  plant. 

''2.  He  showed  that  hybrids  are  commonly  intermediate  between 
their  parents  in  nearly  all  characters  observed,  such  for  example  as 
size  and  shape  of  parts. 

''3.  Many  hybrids  are  partially  or  wholly  sterile,  especially  when 
the  parents  are  very  dissimilar  (belong  to  widely  distinct  species). 
Such  hybrids  often  exceed  either  parent  in  size  and  vigor  of  growth. 

"4.  Kolreuter  did  not  observe  the  regular  splitting  of  hybrids 
which  Mendel  and  De  Vries  record,  but  some  of  his  successors  did, 
particularly  Thomas  Knight  (1799)  and  John  Goss  (1822)  in  England, 

»  Op.  clL,  p.  80, 


HISTORICAL  ACCOUNT  OF  EVOLUTION  THEORY  41 

who  were  engaged  in  crossing  the  garden  peas  with  a  view  to  producing 
more  vigorous  and  productive  varieties,  and  Naudin  (1862)  in  France, 
who  made  a  comprehensive  survey  of  the  facts  of  hybridization  in 
plants  and  came  very  near  to  expressing  the  generaUzation  which 
Mendel  reached  four  years  later." 

Mendel's  law 

"The  earliest  experimental  investigations  of  heredity,"  says 
Locy^  in  a  concise  summary  of  Mendel's  work,  ''were  conducted  with 
'plants,  and  the  first  epoch-making  results  were  those  of  Gregor  Mendel 
(1822-1884),  a  monk  and  later  abbot,  of  an  Augustinian  monastery  at 
Briinn,  Austria.  In  the  garden  of  the  monastery,  for  eight  years 
before  publishing  his  results,  he  made  experiments  on  the  inheritance 
of  individual  (or  unit)  characters  in  twenty-two  varieties  of  garden 
peas.  Selecting  certain  constant  and  obvious  characters,  as  color,  and 
form  of  seed,  length  of  stem,  etc.,  he  proceeded  to  cross  these  pure 
races,  thus  producing  hybrids,  and  thereafter,  to  observe  the  results  of 
self-fertilization  among  the  hybrids. 

''The  hybrids  were  produced  by  removing  the  unripe  stamens  of 
certain  flowers  and  later  fertilizing  them  by  ripe  pollen  from  another 
pure  breed  having  a  contrasting  character.  The  results  showed  that 
only  one  of  a  pair  of  unit  characters  appeared  in  the  hybrid  of  the  next 
generation,  while  the  other  contrasting  character  lay  dormant.  Thus, 
in  crossing  a  yellow-seeded  with  a  green-seeded  pea,  the  hybrid  genera- 
tion showed  only  yellow  seeds.  The  character  thus  impressing  itself 
on  the  entire  progeny  was  called  dominant^  while  the  other  that  was 
held  in  abeyance  was  designated  recessive. 

"That  the"  recessive  color  was  not  blotted  out  was  clearly  demon- 
strated by  allowing  the  hybrid  generation  to  develop  by  self-fertiliza- 
tion. Under  these  circumstances  a  most  interesting  result  was 
attained.  The  filial  generation,  derived  by  self-fertilization  among 
the  hybrids,  produced  plants  with  yellow  and  green  seeds,  but  in  the 
ratio  of  three  yellow  to  one  green.  All  green-seeded  individuals  and 
one-third  of  the  yellow  proved  to  breed  true,  while  the  remaining  two 
thirds  of  the  yellow-seeded  plants,  when  self-fertilized,  produced 
yellow  and  green  seeds  in  the  ratio  of  three  to  one. 

"Subsequent  breedings  gave  an  unending  series  of  results  similar 
to  those  obtained  with  the  first  filial  generation. 

^  William  A.  Locy,  The  Main  Currents  of  Zoology  (Henry  Holt  &  Company, 
1918),  pp.  37-39. 


42         READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

''This  great  principle  of  alternative  inheritance  was  exhibited 
throughout  the  extensive  experiments  of  Mendel,  and  it  is  now  recog- 
nized as  one  of  the  great  biological  discoveries  of  the  nineteenth 
century." 

The  essential  feature  of  Mendel's  discovery  was  not  the  phenome- 
non of  dominance,  for  relatively  few  instances  of  pure  dominance  have 
been  discovered;  but  it  was  the  phenomenon  of  segregation.  By 
segregation  is  meant  that  although  determiners  for  opposed  heredi- 
tary characters  derived  from  diverse  parental  sources  may  unite  in  a 
common  germ  plasm  for  one  generation,  they  segregate  out  pure,  or 
unmodified  by  their  association  together,  in  the  next  and  subsequent 
generations.  This  law  of  segregation  depends  on  the  idea  that  the 
germ  cell  is  composed  of  bundles  of  separately  inheritable  unit  charac- 
ters, which  may  be  paired  or  grouped,  shuffled  and  redealt  like  cards, 
so  as  to  give  an  infinite  number  of  permutations  and  combinations 
without  affecting  the  unit  determiners  themselves. 

From  the  evolutionary  standpoint  it  is  supposed  that  new  unit 
characters  arise  by  mutations  and  are  fully  hereditary.  They  cannot 
be  swamped  out  by  interbreeding  unless  they  are  recessive,  for  they 
will  dominate  the  old  characters.  Even  recessive  characters  could  be 
perpetuated  by  segregation,  or  by  the  union  of  two  individuals  possess- 
ing tlie  determiner  in  the  recessive  condition  as  well  as  the  dominant. 
Thus  a  knowledge  of  the  behavior  of  unit  characters  in  heredity 
reveals  part  of  the  mechanism  for  conserving  new  characters  if  they  are 
advantageous  or  even  sufficiently  fit  to  survive. 

New  types  or  species  might  arise  through  processes  of  hybridiza- 
tion and  the  survival  of  individuals  possessing  the  most  favorable 
combinations  of  characters. 

"Evolution  from  this  point  of  view,"  says  Morgan,^  "has  consisted 
largely  in  introducing  (by  mutations)  new  factors  that  influence 
characters  already  present  in  the  animal  or  plant. 

"Such  a  view  gives  us  a  somewhat  different  picture  of  evolution 
from  the  old  idea  of  a  ferocious  struggle  between  the  individuals  of  a 
species  with  the  survival  of  the  fittest  and  the  annihilation  of  the  less 
fit.  Evolution  assumes  a  more  peaceful  aspect.  New  advantageous 
characters  survive  by  incorporating  themselves  into  the  race,  improv- 
ing it  and  opening  to  it  new  opportunities.  In  other  words,  the 
emphasis  may  be  placed  less  on  the  competition  between  the  indi- 

^  T.  H.  ]\Iorgan,  A  Critique  of  the  Theory  of  Evolution  (Princeton  University 
Press,  1916),  pp.  87,  88. 


HISTORICAL  ACCOUNT  OF  EVOLUTION  THEORY  43 

viduals  of  a  species  (because  the  destruction  of  the  less  fit  does  not 
in  itself  lead  to  anything  that  is  new)  than  on  the  appearance  of  new 
characters  and  modifications  of  old  characters  that  become  incorpo- 
rated in   the  species,   for   on    these   depends  the  evolution  of   the 


race." 


HYBRIDIZATION   AND   THE   ORIGIN    OF    SPECIES 

As  a  consequence  of  the  great  interest  aroused  by  Mendel's 
hybridization  experiments  the  question  has  arisen  as  to  the  role  of 
hybridization  in  organic  evolution.  Certain  it  is  that  a  vast  number 
of  animal  and  plant  races  now  existing  are  mixed  or  hybrid  in  nature 
and  are  continually  sphtting  up  into  various  Mendelian  segregates. 
How  many  pure  races  are  there  today  ?  Some  authors  think  that  no 
variable  races  today  are  pure.  Lotzy  goes  so  far  as  to  claim  and 
attempt  to  prove  that  unit  characters  are  fixed  and  that  the  only 
source  of  variation  is  hybridization,  or  amphimixis.  Biologists  today 
would  not  be  willing  to  go  thus  far  with  Lotzy,  but  it  seems  beyond 
question  that  hybridization  has  played  an  important  role  in  the  pro- 
duction of  very  many  groups  now  living.  It  is  of  interest  to  recall 
that  Linnaeus,  though  a  special  creationist,  admitted  the  possibility 
of  the  origin  of  new  species  by  hybridization. 

NEO-MENDELIAN   DEVELOPMENTS 

Since  the  rediscovery  of  Mendel's  paper  by  De  Vries  and  its  perusal 
by  thousands  of  biologists  the  world  over,  Mendelian  breeding  experi- 
ments with  all  manner  of  animals  and  plants  has  been  the  ruling 
passion  of  geneticists.  Among  the  leading  neo-Mendelians  are  Bate- 
son,  Morgan,  Castle,  Correns,  East,  Hurst,  Shull,  Tschermak,  and  the 
pupils  of  these. 

Perhaps  the  first  two  mentioned,  Bateson  and  Morgan,  have  con- 
tributed most  largely  to  an  understanding  of  the  intricacies  of  the 
Mendelian  operations.  Bateson  has  become  so  imbued  with  the  idea 
that  all  mutations  are  the  result  of  the  loss  of  factors  that  he  proposes 
the  hypothesis  that  ''evolution  has  taken  place  through  the  steady  loss 
of  inhibiting  factors,"  as  Morgan  puts  it.  "Living  matter  was 
stopped  down,  so  to  speak,  at  the  beginning  of  the  world.  As  the 
stops  are  lost,  new  things  emerge.  Living  matter  has  changed  only  in 
that  it  becomes  simpler."  It  is  quite  probable  that  Bateson,  in  pro- 
posing so  radical  a  view,  intended  to  be  taken  only  half-seriously. 
Apart  from  this,  his  best-known  expression  of  opinion,  Bateson  is  the 


44        READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

author  of  a  large  amount  of  fine  work  in  genetics  and  will  rank  high 
in  the  history  of  the  subject. 

T.  H.  Morgan,  our  leading  American  geneticist,  is  best  known  for 
his  researches  into  the  mechanism  of  Mendelian  inheritance.  Through 
the  statistical  study  of  ratios  and  linkages  of  characters  in  the  fruit  fly 
Drosophila,  it  has  been  possible  to  chart  the  localities  of  the  deter- 
miners or  genes  of  at  least  150  mutant  characters.  He  has  shown  that 
four  linked  groups  of  genes  exist,  corresponding  to  the  four  kinds  of 
chromosomes  of  the  germ  cells;  one  of  these  groups  is  sex-linked  and 
is  therefore  to  be  assigned  to  the  X-chromosome  of  the  mutant  male. 
Two  other  large  groups  are  to  be  located  in  the  two  large  autosomes, 
and  one  very  small  group  is  assumed  to  be  located  in  the  microsome. 
Not  only  have  characters,  or  their  determiners,  been  assigned  to  given 
chromosomes,  but  they  have  been  located  in  a  linear  series  on  a  given 
chromosome.  So  accurately  have  these  loci  been  determined  that 
they  may  be  used  to  predict  unknown  breeding  ratios.  It  would 
seem  that  when  a  theory  serves  so  well  that  it  may  be  used  to  predict 
the  results  of  experiments,  such  a  theory  must  be  founded  on  facts. 
Morgan  and  his  collaborators  in  genetics  are  now  convinced  that  they 
have  discovered  the  actual  mechanism  of  heredity  in  the  behavior  of 
the  chromosomes  in  maturation  and  fertilization  and  that  it  is  unex- 
pectedly simple.  Their  views  have  aroused  considerable  opposition, 
but  they  have  met  successfully  all  attacks  up  to  the  present.  If  it  be 
true  that  the  actual  machinery  of  variation  and  heredity  has  been  dis- 
covered, we  are  farther  along  in  our  understanding  of  the  causo- 
mechanical  basis  of  evolution  than  we  could  have  hoped  to  be  at  so 
early  a  date. 

HEREDITY  AND   SEX 

Since  Darwin's  theory  of  sexual  selection,  sex  has  been  a  compli- 
cating factor  in  evolutionary  theories,  and  one  of  the  chief  advances 
of  the  present  century  has  been  in  connection  with  the  factors  con- 
trolling sex  determination  and  sex  differentiation.  The  evolution  of 
sex  has  also  been  a  subject  for  considerable  research. 

It  now  appears  that  sex  is  an  inherited  Mendelian  character,  the 
determiner  of  which  is  carried  in  a  definite  chromosome  or  group 
of  chromosomes.  Cytological  examination  of  germ  cells,  under  the 
able  leadership  of  E.  B.  Wilson,  has  now  made  it  certain  that  sex,  if 
not  directly  the  result  of  the  presence  or  absence  of  specific  chromo- 
somes, at  least  is  absolutely  correlated  with  such  chromosomes.  It 
appears,  however,    that  the  sex  which  is  settled  by  the  chromosome 


HISTORICAL  ACCOUNT  OF  EVOLUTION  THEORY  45 

mechanism  at  the  time  of  fertihzation  may  or  may  not  reaUze  its 
normal  somatic  differentiation,  depending  upon  the  presence  or 
absence  of  the  proper  environment.  Cases  are  on  record  in  which  an 
individual  germinally  determined  as  a  female  may  be  caused  to 
develop  the  secondary  sexual  characters  of  the  male,  or  even  to  pro- 
duce sperms  instead  of  eggs.  A  great  deal  of  extremely  interesting 
work  on  sex  control  and  sex  reversals  has  been  done  within  the  last 
half-dozen  years  and  new  discoveries  are  being  made  almost  daily.  In 
fact,  it  might  be  said  that  the  genetic  study  of  sex  marks  the  high-tide 
level  of  modern  genetic  advance. 

CONCLUDING  REMARKS 

Now  that  we  have  traced  the  evolution  of  the  science  of  organic 
evolution  from  its  crude  beginnings  among  the  Greeks  up  to  the 
present,  we  are  in  a  position  to  go  back  and  make  a  systematic  study 
of  some  of  the  more  important  phases  of  evolutionary  science. 
Charles  Darwin  found  it  necessary  to  prove  the  fact  of  organic  evolu- 
tion before  attempting  to  discover-  its  causes.  His  method  of  proof 
was  to  marshal  a  great  array  of  facts  which  agree  with  the  idea  of 
descent  with  modification;  and  we  shall  follow  Darwin's  method  in 
the  subsequent  chapters  dealing  with  the  evidences  of  evolution. 

Note. — In  the  first  half  of  the  present  historical  account  many  short  passages 
are  presented  in  quotation  marks  without  mentioning  the  source  of  the  quotation. 
In  all  such  cases  it  will  be  understood  that  these  passages  are  from  H.  F.  Osborn's 
book,  From  the  Greeks  to  Darwin  (The  Macmillan  Company). 


CHAPTER  III 

THE   RELATION  OF   EVOLUTION  TO   MATERIALISM^ 

Joseph  Le  Conte 

It  is  seen  in  the  sketch  given  in  the  previous  chapter  that,  after 
every  struggle  between  theology  and  science,  there  has  been  a  read- 
justment of  some  beliefs,  a  giving  up  of  some  notions  which  really  had 
nothing  to  do  with  religion  in  a  proper  sense,  but  which  had  become 
so  associated  with  religious  belief  as  to  be  confounded  with  the  latter — 
a  giving  up  of  some  line  of  defense  which  ought  never  to  have  been 
held  because  not  within  the  rightful  domain  of  theology  at  all.  Until 
the  present  the  whole  difficulty  has  been  the  result  of  misconception, 
and  Christianity  has  emerged  from  every  struggle  only  strengthened 
and  purified,  by  casting  off  an  obstructing  shell  which  hindered  its 
growth.  But  the  present  struggle  seems  to  many  an  entirely  different 
and  far  more  serious  matter.  To  many  it  seems  no  longer  a  struggle 
of  theology,  but  of  essential  religion  itself — a  deadly  life-and-death 
struggle  between  religion  and  materialism.  To  many,  both  skeptics 
and  Christians,  evolution  seems  to  be  synonymous  with  blank  mate- 
rialism, and  therefore  cuts  up  by  the  roots  every  form  of  religion  by 
denying  the  existence  of  God  and  the  fact  of  immortality.  That  the 
enemies  of  religion,  if  there  be  any  such,  should  assume  and  insist  on 
this  identity,  and  thus  carry  over  the  whole  accumulated  evidence  of 
evolution  as  a  demonstration  of  materialism,  although  wholly  unwar- 
ranted, is  not  so  surprising;  but  what  shall  we  say  of  the  incredible 
folly  of  her  friends  in  admitting  the  same  identity! 

A  little  reflection  will  explain  this.  There  can  be  no  doubt  that 
there  is  at  present  a  strong  and  to  many  an  overwhelming  tend- 
ency toward  materialism.  The  amazing  achievements  of  modern 
science;  the  absorption  of  intellectual  energy  in  the  investigation  of 
external  nature  and  the  laws  of  matter  have  created  a  current  in  that 
direction  so  strong  that  of  those  who  feel  its  influence — of  those  who 
do  not  stay  at  home,  shut  up  in  their  creeds,  but  walk  abroad  in  the 
light  of  modern  thought — it  sweeps  away  and  bears  on  its  bosom  all 

^  From  J.  Le  Conte,  Evolution  (copyright  1888).  Used  by  special  permission 
of  the  publishers,  D.  Appleton  &  Company. 

46 


THE  RELATION  OF  EVOLUTION  TO  MATERIALISM  47 

but  the  strongest  and  most  reflective  minds.  Materialism  has  thus 
become  a  fashion  of  thought;  and,  hke  all  fashions,  must  be  guarded 
against.  This  tendency  has  been  created  and  is  now  guided  by 
science.  Just  at  this  time  it  is  strongest  in  the  department  of  biology, 
and  especially  is  evolution  its  stronghold.  This  theory  is  supposed  by 
many  to  be  simply  demonstrative  of  materialism.  Once  it  was  the. 
theory  of  gravitation  which  seemed  demonstrative  of  materialism. 
The  sustentation  of  the  universe  by  law  seemed  to  imply  that  Nature 
operates  itself  and  needs  no  God.  That  time  is  passed.  Now  it  is 
evolution  and  creation  by  law.  This  will  also  pass.  The  theory  seems 
to  many  the  most  materialistic  of  all  scientific  doctrines  only  because 
it  is  the  last  which  is  claimed  by  materialism,  and  the  absurdity  of  the 
claim  is  not  yet  made  clear  to  many. 

The  truth  is,  there  is  no  such  necessary  connection  between  evo- 
lution and  materialism  as  is  imagined  by  some.  There  is  no  dif- 
ference in  this  respect  between  evolution  and  any  other  law  of  Nature. 
In  evolution,  it  is  true,  the  last  barrier  is  broken  down,  and  the 
whole  domain  of  Nature  is  now  subject  to  law;  but  it  is  only  the 
last;  the  march  of  science  has  been  in  the  same  direction  all  the  time. 
In  a  word,  evolution  is  not  only  not  identical  with  materialism,  but, 
to  the  deep  thinker,  it  has  not  added  a  feather's  weight  to  its  proba- 
bility or  reasonableness.  Evolution  is  one  thing  and  materialism 
quite  another.  The  one  is  an  established  law  of  Nature,  the  other  an 
unwarranted  and  hasty  inference  from  that  law.  Let  no  one  imagine, 
as  he  is  conducted  by  the  materialistic  scientist  in  the  paths  of  evo- 
lution from  the  inorganic  to  the  organic,  from  the  organic  to  the 
animate,  from  the  animate  to  the  rational  and  moral,  until  he  lands, 
as  it  seems  to  him,  logically  and  inevitably,  in  universal  material- 
ism— let  no  such  one  imagine  that  he  has  walked  all  the  way  in 
the  domain  of  science.  He  has  stepped  across  the  boundary  into 
the  domain  of  philosophy.  But,  on  account  of  the  strong  tendency 
to  materialism  and  the  skilful  guidance  of  his  leaders,  there  seems 
to  be  no  such  boundary;  he  does  not  distinguish  between  the  induc- 
tions of  science  and  the  inferences  of  a  shallow  philosophy;  the 
whole  is  accredited  to  science,  and  the  final  conclusion  seems  to 
carry  with  it  all  the  certainty  which  belongs  to  scientific  results. 
The  fact  that  these  materiaHstic  conclusions  are  reached  by  some  of 
the  foremost  scientists  of  the  present  day  adds  nothing  to  their 
probabihty.  In  a  question  of  science,  viz.,  the  law  of  evolution,  their 
authority  is  deservedly  high,  but  in  a  question  of  philosophy,  viz., 


48        READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

materialism,  it  is  far  otherwise.  If  the  pure  scientists  smile  when 
theological  philosophers,  unacquainted  with  the  methods  of  science, 
undertake  to  dogmatize  on  the  subject  of  evolution,  they  must 
pardon  the  philosophers  if  they  also  smile  when  the  pure  scientists 
imagine  that  they  can  at  once  solve  questions  in  philosophy  which 
have  agitated  the  human  mind  from  the  earliest  times.  I  am  anxious 
to  show  the  absurdity  of  this  materialistic  conclusion,  but  I  shall  try 
to  do  so,  not  by  any  labored  argument,  but  by  a  few  simple  illustra- 
tions. 

1.  It  is  curious  to  observe  how,  when  the  question  is  concerning  a 
work  of  Nature,  we  no  sooner  find  out  how  a  thing  is  made  than  we 
immediately  exclaim:  "It  is  not  made  at  all,  it  became  so  of  itself!" 
So  long  as  we  knew  not  how  worlds  were  made,  we  of  course  con- 
cluded they  must  have  been  created,  but  so  soon  as  science  showed 
how  it  was  probably  done,  immediately  we  say  we  were  mistaken — 
they  were  not  made  at  all.  So  also,  as  long  as  we  could  not 
imagine  how  new  organic  forms  originated,  we  were  willing  to  believe 
they  were  created,  but,  so  soon  as  we  find  that  they  originated  by 
evolution,  many  at  once  say:  ''We  were  mistaken;  no  creator  is 
necessary  at  all."  Is  this  so  when  the  question  is  concerning  a  work 
of  man?  Yes,  of  one  kind — viz.,  the  work  of  the  magician.  Here, 
indeed,  we  believe  in  him,  and  are  delighted  with  his  work,  until  we 
know  how  it  is  done,  and  then  all  our  faith  and  wonder  cease.  But 
in  any  honest  work  it  is  not  so ;  but  on  the  contrary,  when  we  under- 
stand how  it  is  done,  stupid  wonder  is  changed  into  intellectual 
delight.  Does  it  not  seem,  then,  that  to  most  people  God  is  a  mere 
wonder-worker,  a  chief  magician  ?  But  the  mission  of  science  is  to 
show  us  how  things  are  done.  Is  it  any  wonder,  then,  that  to  such 
persons  science  is  constantly  destroying  their  superstitious  illusions  ? 
But  if  God  is  an  honest  worker,  according  to  reason — i.e.,  according 
to  law — ought  not  science  rather  to  change  gaping  wonder  into 
intelligent  delight,  superstition  into  rational  worship  ? 

2.  Again,  it  is  curious  to  observe  how  an  old  truth,  if  it  come  only 
in  a  new  form,  often  strikes  us  as  something  unheard  of,  and  even  as 
paradoxical  and  almost  impossible.  A  little  over  thirty  years  ago  a 
little  philosophical  toy,  the  gyroscope,  was  introduced  and  became 
very  common.  At  first  sight,  it  seems  to  violate  all  mechanical  laws 
and  set  at  naught  the  law  of  gravitation  itself.  A  heavy  brass  wheel, 
four  to  five  inches  in  diameter,  at  the  end  of  a  horizontal  axle,  six  or 
eight  inches  long,  is  set  rotating  rapidly,  and  then  the  free  end  of  the 


THE  RELATION  OF  EVOLUTION  TO  MATERIALISM  49 

axis  is  supported  by  a  string  or  otherwise.  The  wheel  remains 
suspended  in  the  air  while  slowly  gyrating.  What  mysterious  force 
sustains  the  wheel  when  its  only  point  of  support  is  at  the  end  of  the 
axle,  six  or  eight  inches  away  ?  Scientific  and  popular  literature  were 
flooded  with  explanations  of  this  seeming  paradox.  And  yet  it  was 
nothing  new.  The  boy's  top,  that  spins  and  leans  and  will  not  fall, 
although  solicited  by  gravity,  so  long  as  it  spins,  which  we  have  seen 
all  our  lives  without  special  wonder,  is  precisely  the  same  thing. 

Now,  evolution  is  no  new  thing,  but  an  old  familiar  truth;  but, 
coming  now  in  a  new  and  questionable  shape,  lo,  how  it  startles  us  out 
of  our  propriety !  Origin  of  forms  by  evolution  is  going  on  everywhere 
about  us,  both  in  the  inorganic  and  the  organic  world.  In  its  more 
familiar  forms,  it  had  never  occurred  to  most  of  us  that  it  was  a 
scientific  refutation  of  the  existence  of  God,  that  it  was  a  demonstra- 
tion of  materialism.  But  now  it  is  pushed  one  step  farther  in  the 
direction  it  has  always  been  going — it  is  made  to  include  also  the  origin 
of  species — only  a  little  change  in  its  form,  and  lo,  how  we  start!  To 
the  deep  thinker,  now  and  always,  there  is  and  has  been  the  alterna- 
tive— materialism  or  theism.  God  operates  Nature  or  Nature 
operates  itself;  but  evolution  puts  no  new  phase  on  this  old  question. 
For  example,  the  origin  of  the  individual  by  evolution.  Everybody 
knows  that  every  one  of  us  individually  became  what  we  now  are  by  a 
slow  process  of  evolution  from  a  microscopic  spherule  of  protoplasm, 
and  yet  this  did  not  interfere  with  the  idea  of  God  as  our  individual 
maker.  Why,  then,  should  the  discovery  that  the  species  (or  first 
individuals  of  each  kind)  originated  by  evolution  destroy  our  belief 
in  God  as  the  creator  of  species  ? 

3.  It  is  curious  and  very  interesting  to  observe  the  manner  in 
which  vexed  questions  are  always  finally  settled,  if  settled  at  all. 
All  vexed  questions — i.e.,  questions  which  have  taxed  the  powers  of 
the  greatest  minds  age  after  age — are  such  only  because  there  is  a  real 
truth  on  both  sides.  Pure,  unmixed  error  does  not  five  to  plague  us 
long.  Error,  when  it  continues  to  live,  does  so  by  virtue  of  a  germ  of 
truth  contained.  Great  questions,  therefore,  continue  to  be  argued 
pro  and  con  from  age  to  age,  because  each  side  is  in  a  sense — i.e., 
from  its  own  point  of  view — true,  but  wrong  in  excluding  the  other 
point  of  view;  and  a  true  solution,  a  true  rational  philosophy,  will 
always  be  found  in  a  view  which  combines  and  reconciles  the  two 
partial,  mutually  excluding  views,  showing  in  what  they  are  true  and 
in  what  they  are  false — explaining  their  differences  by  transcending 


50        READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

them.  This  is  so  universal  and  far-reaching  a  principle  that  I  am  sure 
I  will  be  pardoned  for  illustrating  it  in  the  homeliest  and  tritest  fashion. 
I  will  do  so  by  means  of  the  shield  with  the  diverse  sides,  giving  the 
story  and  construing  it,  however,  in  my  own  way.  There  is,  appar- 
ently, no  limit  to  the  amount  of  rich  marrow  of  truth  that  may  be 
extracted  from  these  dry  bones  of  popular  proverbs  and  fables  by 
patient  turning  and  gnawing. 

We  all  remember,  then,  the  famous  dispute  concerning  the  shield, 
with  its  sides  of  different  colors,  which  we  shall  here  call  white  and 
black.  We  all  remember  how,  after  vain  attempts  to  discover  the 
truth  by  dispute,  it  was  agreed  to  try  the  scientific  method  of  investi- 
gation. We  all  remember  the  surprising  result.  Both  parties  to  the 
dispute  were  right  and  both  were  wrong.  Each  was  right  from  his 
point  of  view,  but  wrong  in  excluding  the  other  point  of  view.  Each 
was  right  in  what  he  asserted,  and  each  wrong  in  what  he  denied. 
And  the  complete  truth  was  the  combination  of  the  partial  truths  and 
the  elimination  of  the  partial  errors.  But  we  must  not  make  the  mis- 
take of  supposing  that  truth  consists  in  compromise.  There  is  an  old 
adage  that  truth  lies  in  the  middle  between  antagonistic  extremes. 
But  it  seems  to  us  that  this  is  the  place  of  safety,  not  of  truth.  This  is 
the  favorite  adage,  therefore,  of  the  timid  man,  the  time-server,  the 
fence-man,  not  the  truth-seeker.  Suppose  there  had  been  on  the 
occasion  mentioned  above  one  of  these  fence-philosophers.  He  would 
have  said:  "These  disputants  are  equally  intelligent  and  equally 
valiant.  One  side  says  the  shield  is  white,  the  other  that  it  is  black; 
now  truth  lies  in  the  middle;  therefore,  I  conclude  the  shield  is  gray  or 
neutral  tint,  or  a  sort  of  pepper-and-salt. "  Do  we  not  see  that  he  is 
the  only  man  who  has  no  truth  in  him?  No;  truth  is  no  hetero- 
geneous mixture  of  opposite  extremes,  but  a  stereoscopic  combination 
of  two  surface  views  into  one  solid  reality. 

Now,  the  same  is  true  of  all  vexed  questions,  and  I  have  given  this 
trite  fable  again  only  to  apply  it  to  the  case  in  hand. 

There  are  three  possible  views  concerning  the  origin  of  organic 
forms  whether  individual  or  specific.  Two  of  these  are  opposite 
and  mutually  excluding;  the  third  combining  and  reconciling.  For 
example,  take  the  individual.  There  are  three  theories  concerning 
the  origin  of  the  individual.  The  first  is  that  of  the  pious  child  who 
thinks  that  he  was  made  very  much  as  he  himself  makes  his  dirt-pies; 
the  second  is  that  of  the  street-gamin,  or  of  Topsy,  who  says:  "I  was 
not  made  at  all,  I  growed'';    the  third  is  that  of  most  intelligent 


THE  RELATION  OF  EVOLUTION  TO  MATERIALISM  51 

Christians — i.e.,  that  we  were  made  by  a  process  of  evolution.  Observe 
that  this  latter  combines  and  reconciles  the  other  two,  and  is  thus  the 
more  rational  and  philosophical.  Now,  there  are  also  three  exactly 
corresponding  theories  concerning  the  origin  of  species.  The  first  is 
that  of  many  pious  persons  and  many  intelligent  clergymen,  who  say 
that  species  were  made  at  once  by  the  Divine  hand  without  tiatural 
process.  The  second  is  that  of  the  materialists,  who  say  that  species 
were  not  made  at  all,  they  were  derived,  '^they  growed."  The  third 
is  that  of  the  theistic  evolutionists,  who  think  that  they  were  created 
by  a  process  of  evolution — who  believe  that  making  is  not  incon- 
sistent with  growing.  The  one  asserts  the  divine  agency,  but 
denies  natural  process;  the  second  asserts  the  natural  process,  but 
denies  divine  agency;  the  third  asserts  divine  agency  by  natural  process. 
Of  the  first  two,  observe,  both  are  right  and  both  wrong;  each  view  is 
right  in  what  it  asserts,  and  wrong  in  what  it  denies — each  is  right 
from  its  own  point  of  view,  but  wrong  in  excluding  the  other  point 
of  view.  The  third  is  the  only  true  rational  solution,  for  it  includes, 
combines,  and  reconciles  the  other  two;  showing  wherein  each  is  right 
and  wherein  wrong.  It  is  the  combination  of  the  two  partial  truths, 
and  the  elimination  of  the  partial  errors.  But  let  us  not  fail  to  do 
perfect  justice.  The  first  two  views  of  origin,  whether  of  the  indi- 
vidual or  of  the  species,  are  indeed  both  partly  wrong  as  well  as 
partly  right;  but  the  view  of  the  pious  child  and  of  the  Christian  con- 
tains by  far  the  more  essential  truth.  Of  the  two  sides  of  the  shield, 
theirs  is  at  least  the  whiter  and  more  beautiful. 

But,  alas!  the  great  bar  to  a  speedy  settlement  of  this  question  and 
the  adoption  of  a  rational  philosophy  is  not  in  the  head,  but  in  the 
heart — is  not  in  the  reason,  but  in  pride  of  opinion,  self-conceit, 
dogmatism.  The  rarest  of  all  gifts  is  a  truly  tolerant,  rational  spirit. 
In  all  our  gettings  let  us  strive  to  get  this,  for  it  alone  is  true  wisdom. 
But  we  must  not  imagine  that  all  the  dogmatism  is  on  one  side,  and 
that  the  theological.  Many  seem  to  think  that  theology  has  sl''  pre- 
emptive right''  to  dogmatism.  If  so,  then  modern  materialistic  science 
has  "jumped  the  claim.''  Dogmatism  has  its  roots  deep-bedded  in  the 
human  heart.  It  showed  itself  first  in  the  domain  of  theology,  because 
there  was  the  seat  of  power.  In  modern  times  it  has  gone  over  to  the 
side  of  science,  because  here  now  is  the  place  of  power  and  fashion. 
There  are  two  dogmatisms,  both  equally  opposed  to  the  true  rational 
spirit,  viz.,  the  old  theological  and  the  new  scientific.  The  old  clings 
fondly  to  old  things,  only  because  they  are  old;  the  new  grasps  eagerly 


52         READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

after  new  things,  only  because  they  are  new.  True  wisdom  and  true 
philosophy,  on  the  contrary,  tries  all  things  both  old  and  new,  and 
holds  fast  only  to  that  which  is  good  and  true.  The  new  dogmatism 
taunts  the  old  for  credulity  and  superstition;  the  old  reproaches  the 
new  for  levity  and  skepticism.  But  true  wisdom  perceives  that  they 
are  both  equally  credulous  and  equally  skeptical.  The  old  is  credulous 
of  old  ideas  and  skeptical  of  new;  the  new  is  skeptical  of  old  ideas  and 
credulous  of  new.  Both  deserve  the  unsparing  rebuke  of  all  right- 
minded  men.  The  appropriate  rebuke  for  the  old  dogmatism  has 
been  already  put  in  the  mouth  of  Job  in  the  form  of  a  bitter  sneer : 
"No  doubt  ye  are  the  people,  and  wisdom  shall  die  with  you."  The 
appropriate  rebuke  for  the  new  dogmatism,  though  not  put  into 
the  mouth  of  any  ancient  prophet,  ought  to  be  uttered — I  will  under- 
take to  utter  it  here.  I  would  say  to  these  modern  materialists, 
''No  doubt  ye  are  the  men,  and  wisdom  and  true  philosophy  were 
horn  with  you." 

Let  it  be  observed  that  we  are  not  here  touching  the  general  ques- 
tion of  the  personal  agency  of  God  in  operating  Nature.  This  we  shall 
take  up  hereafter.  All  that  we  wish  to  insist  on  now  is  that  the  process 
and  the  law  of  evolution  does  not  differ  in  its  relation  to  materialism 
from  all  other  processes  and  laws  of  Nature.  If  the  sustentation  of 
the  universe  by  the  law  of  gravitation  does  not  disturb  our  belief  in 
God  as  the  sustainer  of  the  universe,  there  is  no  reason  why  the  origin 
of  the  universe  by  the  law  of  evolution  should  disturb  our  faith  in  God 
as  the  creator  of  the  universe.  If  the  law  of  gravitation  be  regarded 
as  the  Divine  mode  of  sustentation,  there  is  no  reason  why  we  should 
not  regard  the  law  of  evolution  as  the  Divine  process  of  creation.  It 
is  evident  that  if  evolution  be  materialism,  then  is  gravitation  also 
materialism;  then  is  every  law  of  Nature  and  all  science  materialism. 
If  there  be  any  difference  at  all,  it  consists  only  in  this :  that,  as  already 
said,  here  is  the  last  line  of  defense  of  the  supporters  of  supernatural- 
ism  in  the  realm  of  Nature.  But  being  the  last  line  of  defense — 
the  last  ditch — it  is  evident  that  a  yielding  here  implies  not  a  mere 
shifting  of  line,  but  a  change  of  base;  not  a  readjustment  of  details 
only,  but  a  reconstruction  of  Christian  theology.  This,  I  believe,  is 
indeed  necessary.  There  can  be  little  doubt  in  the  mind  of  the 
thoughtful  observer  that  we  are  even  now  on  the  eve  of  the  greatest 
change  in  traditional  views  that  has  taken  place  since  the  birth  of 
Christianity.  But  let  no  one  be  greatly  disturbed  thereby.  For 
then,  so  now,  change  comes  not  to  destroy  but  to  fulfil  all  our  dearest 


THE  RELATION  OF  EVOLUTION  TO  MATERIALISM  53 

hopes  and  aspirations;  as  then,  so  now,  the  germ  of  living  truth  has, 
in  the  course  of  ages,  become  so  encrusted  with  meaningless  traditions 
which  stifle  its  growth  that  it  is  necessary  to  break  the  shell  to  set  it 
free;  as  then,  so  now,  it  has  become  necessary  to  purge  religious  belief 
of  dross  in  the  form  of  trivialities  and  superstitions.  This  has  ever  been 
and  ever  will  be  the  function  of  science.  The  essentials  of  religious 
faith  it  does  not,  it  cannot,  touch,  but  it  purifies  and  ennobles  our 
conceptions  of  Deity,  and  thus  elevates  the  whole  plane  of  religious 
thought. 


PART  II 
EVIDENCES  OF  ORGANIC  EVOLUTION 


CHAPTER  IV 

IS  ORGANIC  EVOLUTION  AN  ESTABLISHED  PRINCIPLE  ? 

H.  H.  Newman 

1.  Is  there  definite  proof  of  organic  evolution  ? 

2.  If  so,  what  is  the  nature  of  the  proof  ? 

3.  What  are  the  evidences  of  evolution,  and  in  what  ways  do  these 
bear  witness  that  evolution  has  occurred  and  is  still  occurring  ? 

Before  presenting  in  any  detail  the  several  bodies  of  data  that 
constitute  the  "evidences  of  evolution,"  let  us  anticipate  a  little  by 
attempting  to  answer  the  three  questions  just  propounded. 

I.  Reluctant  as  he  may  be  to  admit  it,  honesty  compels  the 
evolutionist  to  admit  that  there  is  no  absolute  proof  of  organic 
evolution.  But,  for  that  matter,  there  is  no  absolute  proof  of  any- 
thing that  depends  on  records  of  past  events.  We  have  no  absolute 
proof  that  Caesar  or  Napoleon  once  lived,  or  fought,  or  conquered. 
All  we  have  are  the  accounts  left  by  the  historians  which  we  accept 
without  question  because  they  are  the  products  of  human  thought  and 
imagination.  There  is  no  absolute  proof  for  either  of  the  more  or  less 
directly  opposed  theories  of  the  origin  of  the  material  universe:  the 
''nebular  hypothesis"  of  Laplace,  and  the  " planetesimal  hypothesis" 
of  Chamberlin  and  Moulton.  Both  of  these  theories  rest  upon 
exactly  the  same  types  of  evidences  as  does  the  theory  of  organic  evolu- 
tion, viz.,  the  amassing  of  facts  which  appear  to  be  explicable  on  the 
assumption  that  the  one  or  the  other  theory  is  true.  If  all  of  the  facts 
are  in  accord  with  it,  and  none  are  found  that  are  incapable  of  being 
reconciled  with  it,  a  working  hypothesis  is  said  to  have  been  advanced 
to  the  rank  of  a  proved  theory.  As  yet  it  is  impossible  to  say  that 
either  of  these  theories  as  to  the  origin  of  the  universe  has  been  proved. 
Yet  there  is  much  less  popular  opposition  to  the  acceptance  of  these 
theories  as  facts  than  there  is  to  the  general  theory  of  organic  evolu- 
tion. Similarly,  there  are  certain  widely  accepted  theories  of  the 
origin  of  the  present  conditions  of  the  earth's  crust,  and  its  liquid  and 
gaseous  envelopes.  The  accepted  theory,  as  given  us  by  Hut  ton  and 
especially  by  Lyell,  is  essentially  an  evolutionary  theory  and  depends 
for  its  proof  on  almost  exactly  the  same  types  of  evidence  as  does  that 

57 


58        READINGS  IX  EVOLUTION,  GENETICS,  AND  EUGENICS 

of  organic  evolution.  The  basis  of  the  accepted  theory  of  geological 
evolution  is  the  " uniformitarian  doctrine"  of  Lyell,  which  assumes 
that  the  key  to  the  past  lies  in  the  present,  that  the  changes  that  are 
going  on  today  are  of  the  same  order  and  kind  as  those  of  the  past, 
and,  finally,  that  there  is  neither  beginning  nor  end  to  the  earth's 
evolutionary  history,  but  that  a  slow  and  orderly  development  has 
gone  on  and  will  continue  indefinitely.  The  proof  of  this  conception 
consists  of  an  array  of  facts  derived  from  a  study  of  the  earth's  crust, 
including  its  stratified  structure,  of  traces  of  animal  and  plant  life 
preserved  in  the  rocks,  of  observed  changes  in  continental  contours 
going  on  today,  of  erosion  going  on  in  coasts  and  streams,  and  of  a 
considerable  array  of  facts  derived  from  a  study  of  other  worlds  than 
ours  in  the  making.  The  theory  of  geologic  evolution  meets  with 
scarcely  any  opposition  today,  although  its  foundations  are  no  more 
securely  based  than  are  those  of  organic  evolution. 

In  a  sense  the  proofs  of  the  atomic,  ionic,  and  electron  theories 
are  even  less  absolutely  estabhshed  than  is  that  of  organic  evolution, 
because  no  one  has  ever  seen  nor  ever  can  see  an  atom,  an  ion,  or  an 
electron.  Chemical  and  physical  facts  are  rationalized  by  assuming 
the  existence  of  these  units  with  their  various  properties.  The  only 
evidences  of  the  existence  of  atoms,  ions,  and  electrons  appear  in  the 
facts  that,  on  the  assumption  that  they  exist,  the  whole  array  of 
observed  chemical  and  physical  phenomena  are  rationalized  and 
bound  together  into  a  coherent,  consistent,  and  intelligible  system. 
In  other  words,  with  the  atomic,  ionic,  and  electron  theories  chemistry 
and  physics  are  highly  rational  sciences;  without  these  theories  the 
phenomena  of  physics  and  chemistry  would  be  a  hopeless  hodgepodge. 
Yet  who  would  say  that  these  fundamental  theories  are  absolutely 
proved  ? 

The  only  type  of  proof  of  phenomena  that  cannot  be  directly 
observed  or  that  pertain  to  the  remote  past  is  circumstantial  proof. 
By  analogy  we  conclude  that  certain  changes  took  place  thus  and  so 
in  the  past  because  we  observe  similar  changes  going  on  today.  Every 
past  event  has  left  a  trace,  and  it  is  the  task  of  the  historian,  anti- 
quarian, or  evolutionist  to  discover  and  to  interpret  these  traces.  Some- 
times the  traces  exist  as  vestiges  in  modern  life  and  are  meaningless 
unless  related  to  their  origin  in  the  past.  The  task  of  the  student  of 
organic  evolution  is  to  gather  all  of  the  traces  of  past  changes  both  in 
living  creatures  today  and  in  the  preserved  remains  of  creatures  of  the 
remote  past.     A  collection  of  traces  of   evolution  involves   many 


IS  ORGANIC  EVOLUTION  ESTABLISHED  ? 


59 


apparently  unrelated  bodies  of  phenomena.  There  are  evidences  of 
evolution  in  the  grouping  of  animals  into  phyla,  classes,  orders, 
families,  genera,  species,  varieties,  and  races;  in  the  homologies  that 
exist  in  general  structure  and  in  particular  organs  between  different 
groups  of  animals  and  plants;  in  the  orderly  process  of  ontogeny  or 
embryonic  development  of  the  individual;  in  actual  blood  relation- 
ship, based  upon  chemical  reactions;  on  the  succession  of  extinct 
animals  and  plants  found  as  fossils  imbedded  in  the  geologic  strata; 
in  the  present  geographical  distribution  of  the  various  groups  of 
animals  and  plants,  in  the  light  of  data  derived  from  a  study  of 
geological  changes;  and  finally,  in  experimental  evolution,  which 
involves  the  observation  under  experimental  control  of  changes  in 
organisms  and  the  origin  of  new  varieties  or  elementary  species. 

2.  The  nature  of  the  proof  of  organic  evolution,  then,  is  this: 
that,  using  the  concept  of  organic  evolution  as  a  working  hypothesis 
it  has  been  possible  to  rationalize  and  render  intelligible  a  vast  array 
of  observed  phenomena,  the  real  facts  upon  which  evolution  rests. 
Thus  classification  (taxonomy),  comparative  anatomy,  embryology, 
palaeontology,  zoogeography  and  phytogeography,  serology,  genetics, 
become  consistent  and  orderly  sciences  when  based  upon  evolu- 
tionary foundations,  and  when  viewed  in  any  other  way  they  are 
thrown  into  the  utmost  confusion.  There  is  no  other  generalization 
known  to  man  which  is  of  the  least  value  in  giving  these  bodies  of 
fact  any  sort  of  scientific  coherence  and  unity.  In  other  words,  the 
working  hypothesis  works  and  is  therefore  acceptable  as  truth  until 
overthrown  by  a  more  workable  hypothesis.  Not  only  does  the 
hypothesis  work,  but,  with  the  steady  accumulation  of  further  facts, 
the  weight  of  evidence  is  now  so  great  that  it  overcomes  all  intelligent 
opposition  by  its  sheer  mass.  There  are  no  rival  hypotheses  except 
the  outworn  and  completely  refuted  idea  of  special  creation,  now 
retained  only  by  the  ignorant,  the  dogmatic,  and  the  prejudiced. 

3.  In  answer  to  the  question,  ''What  are  the  evidences  of  evolution 
and  in  what  ways  do  these  bear  witness  that  evolution  has  occurred 
and  is  still  occurring?"  we  may  present  an  ordered  hst  of  subjects 
that  are  to  be  taken  up  serially  in  detail.  In  connection  with  each  of 
these  bodies  of  evidence  the  character  of  their  witness-bearing  will  be 
discussed. 

Some  of  the  evidences  are  more  direct  and  freer  from  purely  inter- 
pretative construction  than  others.  Some  evidences  are  primary  and 
foundational;  some  are  in  themselves  rather  inconclusive,  but  serve 


6o        REx\DIXGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

to  confirm  other  facts,  and,  when  reinforced  by  other  evidences,  are 
themselves  strongly  substantiated.  Perhaps  the  crowning  evidence 
of  the  truth  of  evolution  is  that  all  of  these  diverse  bodies  of  phenomena 
invariably  support  one  another  and  all  point  in  the  same  direction  and 
to  the  same  conclusion,  viz.,  that  organic  evolution  is  a  fact. 

In  presenting  the  evidences  of  evolution,  those  evidences  that  are 
believed  to  furnish  the  most  direct  proof  are  discussed  first  and  those 
whose  evidence  is  subsidiary  and  confirmatory  are  dealt  with  later. 
The  order  of  treatment,  therefore,  will  be  as  follows: 

I.  Palaeontology — the  evidence  afforded  by  a  study  of  the  dis- 
tribution in  time  (vertical  distribution  in  the  earth's  strata)  of  the 
fossil  remains  of  extinct  animals  and  plants. 

II.  Geographic  distribution — the  evidence  afforded  by  present 
(also,  to  some  extent,  past)  horizontal  distribution  of  contemporaneous 
animals  and  plants. 

III.  Classification — the  evidence  that  the  present  groups  of 
animals  and  plants  have  arisen  by  ''descent  with  modification," 
which  is  an  evolutionary  conception. 

IV.  Comparative  anatomy  {homologies  and  vestigial  structures) — • 
the  evidence  derived  from  the  fact  that  structures  in  unlike  organisms 
have  a  common  plan  and  mode  of  origin;  that  changes  have  occurred 
which  are  in  some  way  related  to  changes  of  habit  or  of  environment. 

V.  Serology  {blood-transfusion  tests) — the  evidence  that  the 
chemical  specificity  of  the  blood  parallels  taxonomic  specificity. 

VI.  Ejnbryology  {the  doctrine  of  recapitulation) — the  evidence  that 
the  embryonic  development  of  the  individual  follows  the  main  outlines 
of  the  evolutionary  history  of  its  ancestors. 

VII.  Experimental  evolution  {genetics) — evidences  that  heritable 
variations  can  be  produced  experimentally  and  that  these  are  of  the 
same  general  character  as  those  which  occur  spontaneously  in  Nature. 
(This  material  will  be  presented  in  some  detail  in  Part  IV  of  this 
book.) 


CHAPTER  V 
EVIDENCES  FROM  PALAEONTOLOGY 

STRENGTH  AND  WEAKNESS  OF  THE  EVIDENCE 

[The  word  palaeontology  means  literally  the  science  of  ancient 
life.  Practically,  it  is  the  study  of  the  fossil  remains  of  extinct  animals 
and  plants,  including  any  traces  of  their  existence,  such  as  footprints, 
impressions  in  slate,  clay,  or  coal.  The  evidence  from  the  fossils  has 
definite  elements  of  strength  in  that  it  deals  with  actual  organisms  that 
formerly  inhabited  the  earth's  surface.  Many  of  these  species  must 
have  left  descendants,  some  of  which  are  doubtless  living  in  a  modified 
condition  today.  Palaeontology  should  be  able  either  strongly  to 
support  or  to  contradict  the  idea  of  evolution.  If  its  data  accord  with 
the  evolution  idea  and  are  opposed  to  the  special  creation  idea,  the 
fossils  may  be  said  to  be  evidences  of  evolution. 

The  weakness  of  the  study  of  fossils  lies  in  the  fact  that  extremely 
few  samples  of  the  living  forms  that  have  existed  in  the  past  have 
been  preserved,  and  of  those  that  have  been  preserved  only  a  very 
small  percentage  have  been  dug  up  and  studied  by  capable  scientists. 
Many  types  of  animals  and  plants,  moreover,  are  soft  and  capable 
of  preservation  only  under  such  exceptional  conditions  that  but 
a  rare  specimen  here  and  there  over  the  world,  scattered  through 
various  widely  separated  strata,  has  been  found.  Only  very  common 
or  abundant  types  are  likely  to  have  been  preserved  and  discovered, 
for  the  chances  of  an  uncommon  form  being  preserved  would  be  small 
and  the  further  chances  of  these  infrequently  preserved  specimens 
being  found  woul  d  be  infinitely  smaller. 

The  great  majority  of  fossil  remains  are  fragmentary  or  preserved 
very  incompletely,  so  that  only  the  hard  parts  have  come  down 
to  us.  There  are,  of  course,  many  important  exceptions  to  this  rule, 
and  these  are  our  chief  reliance  in  interpreting  ancient  life. 

That  Darwin  fully  realized  the  vulnerable  points  in  the  palaeonto- 
logical  record  is  shown  by  the  following  quotation  from  the  Origin  of 
Species: — Ed.] 

''I  look  at  the  geological  record  as  a  history  of  the  world  imper- 
fectly kept  and  written  in  a  changing  dialect;  of  this  history  we  possess 

6i 


62        READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

the  last  volume  alone,  relating  only  to  two  or  three  countries.  Of 
this  volume  only  here  and  there  a  short  chapter  has  been  preserved; 
and  of  each  page  only  here  and  there  a  few  lines.  Each  word  of  the 
slowly  changing  language,  more  or  less  different  in  the  successive 
chapters,  may  represent  the  forms  of  life  which  are  entombed  in  our 
successive  formations  and  which  falsely  appear  to  us  to  have  been 
abruptly  introduced." 

OTHER  OPINIONS  AS  TO  THE  ADEQUACY  OF  THE  EVIDENCES 

OF  PALAEONTOLOGY 

''The  primary  and  direct  evidence  in  favour  of  evolution  can  be 
furnished  only  by  palaeontology.  The  geological  record,  so  soon  as 
it  approaches  completeness,  must,  when  properly  questioned,  yield 
either  an  affirmative  or  a  negative  answer:  if  Evolution  has  taken 
place  there  will  its  mark  be  left;  if  it  has  not  taken  place  there  will 
lie  its  refutation." — T.  H.  Huxley. 

"The  geological  record  is  not  so  hopelessly  incomplete  as  Darwin 
believed  it  to  be.  Since  The  Origin  of  Species  was  written  our  knowl- 
edge of  that  record  has  been  enormously  extended,  and  we  now  possess 
no  complete  volumes,  it  is  true,  but  some  remarkably  full  and  illumi- 
nating chapters.  The  main  significance  of  the  whole  lies  in  the  fact 
ihdii,  just  in  proportion  to  the  completeness  of  the  record  is  the  unequivocal 
character  of  its  testimony  to  the  truth  of  the  evolutionary  theory. ^^ — 
W.  B.  Scott. 

''On  the  other  hand,  matters  have  greatly  improved  since  Darwin 
wrote  his  oft-cited  Chapter  X;  many  lands  then  geologically  unknown 
have  been  explored  and  many  of  the  missing  chapters  and  paragraphs 
in  the  history  of  life  have  been  brought  to  light.  The  most  ancient 
biologically  intelligible  period  of  the  earth's  history  is  called  the 
Cambrian  and,  compared  with  the  succeeding  periods,  the  Cambrian 
has  always  been  poor  in  fossils,  great  areas  and  thicknesses  of  rocks 
being  entirely  barren.  No  one  could  doubt  that  our  knowledge  of 
Cambrian  life  was  most  incomplete  and  inadequate.  A  few  years  ago 
Dr.  C.  D.  Walcott,  Secretary  of  the  Smithsonian  Institution,  dis- 
covered in  the  Canadian  Rockies  a  most  marvelous  series  of  Cambrian 
fossils  of  an  incredible  delicacy  and  beauty  of  preservation,  which 
have  thrown  a  flood  of  new  and  unexpected  light  into  very  dark  places. 
It  is  clear  that  the  Cambrian  seas  swarmed  with  a  great  variety  and 
profusion  of  life,  but  that  in  only  a  few  places,  so  far  known  to  us, 


EVIDENCES  FROM  PALAEONTOLOGY  63 

* 

were  conditions  such  that  these  delicate  creatures  could  be  preserved. 
It  is  not  possible  to  say  how  far  the  difficulty  caused  by  the  imperfec- 
tion of  the  geological  record  will  be  removed  by  the  progress  of  dis- 
covery. Even  as  matters  stand  to-day,  the  astonishing  fact  is  that 
so  much  has  been  preserved,  rather  than  that  the  story  is  so  incom- 
plete. Notwithstanding  all  the  difficulties,  the  palaeontological 
method  remains  one  of  the  most  valuable  means  of  testing  the  theory 
of  evolution,  because  certain  chapters  in  the  history  of  life  have  been 
recorded  with  a  minuteness  that  is  really  very  surprising." — 
W.  B.  Scott,  Theory  of  Evolution,  (The  Macmillan  Company.  Re- 
printed by  permission). 

WHAT   FOSSILS   ARE   AND   HOW   THEY   HAVE   BEEN   PRESERVED 

*'  Fossils  are  only  animals  and  plants  which  have  been  dead  rather 
longer  than  those  which  died  yesterday." — T.  H.  Huxley. 

"Fossils  are  either  actual  remains  of  bones  or  other  parts  preserved 
intact  in  soil  or  rocks,  or  else,  and  more  commonly,  parts  of  animals 
which  have  been  turned  into  stone,  or  of  which  stony  casts  have  been 
made.  All  such  remains  buried  by  natural  causes  are  called  fossils." — 
Jordan  and  Kellogg. 

FOSSILS    CLASSIFIED 

[Class  I.  The  actual  remains  of  recently  extinct  animals  and 
plants  which  have  been  buried  or  surrounded  by  some  sort  of  preserv- 
ing material  constitute  the  first  type  under  consideration.  Such 
remains  have  undergone  little  or  no  change  of  the  original  organic 
matter  into  inorganic.  Thus  we  find  the  complete  bodies  of  great 
hairy  mammoths  frozen  in  the  arctic  ice.  These  are  so  well  preserved 
that  dogs  have  fed  upon  their  flesh.  Nearly  a  thousand  species  of 
extinct  insects,  including  many  ants,  have  been  obtained  practically 
intact  from  amber,  a  form  of  petrified  resin.  Innumerable  mollusk 
shells,  teeth  of  sharks,  pieces  of  buried  logs,  bones  of  animals  buried 
in  asphalt  lakes  and  bogs,  have  been  found  in  a  well-preserved 
condition. 

Class  2.  Petrified  fossils. — The  process  of  petrification  involves 
the  replacement,  particle  for  particle,  of  the  organic  matter  of  a  dead 
animal  or  plant  by  mineral  matter.  So  completely  is  the  finer 
structure  preserved  that  microscopic  sections  of  preserved  tissues, 
especially  of  plants,  have  practically  the  same  appearance  as  sections 
.made  from  living  organisms.  Various  mineral  materials  have  been 
employed  in  petrification,  such  as  quartz,  hmestone,  or  iron  pyrites. 


64       READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

* 

Class  3.  Casts  and  impressions. — Very  frequently  the  animal  or 
plant  has  been  buried  in  mud  or  has  lain  on  a  soft  mud  flat  only 
long  enough  to  have  left  its  impress  in  the  plastic  material.  Sub- 
sequently the  entire  organism  has  decayed  and  been  dissolved  away, 
and  its  place  has  been  taken  by  a  mineral  deposit.  Thus  only  the 
external  appearance  has  been  preserved,  as  would  be  the  case  in 
making  plaster-of-paris  casts.  Sometimes  traceries  of  soft-bodied 
animals  have  been  left  upon  forming  slate  or  coal  that  are  almost  as 
accurate  in  detail  as  a  lithograph. 

Perhaps  the  most  remarkable  fossils  known  are  those  found  by 
Professor  Charles  D.  Walcott  in  the  marine  oily  shales  of  British 
Columbia.  A  large  number  of  soft-bodied  invertebrates  of  Cambrian 
age  have  been  found  so  wonderfully  preserved  that  not  only  are 
the  external  features  revealed,  but  sometimes  even  the  details  of 
the  internal  organs  may  be  seen  through  the  transparent  integu- 
ment. 

Some  authorities  include  among  fossils  such  traces  of  extinct  life 
as  footprints,  utensils  and  tools  of  extinct  man,  and  even  the 
vestiges  of  archaic  sea  beaches.  Perhaps  this  is  stretching  the 
definition  of  the  term  "fossil"  too  far. — Ed.] 

ON   THE   CONDITIONS   NECESSARY   FOB,  EOSSILIZATION 

"Examination  and  study  of  the  rocks  of  the  earth  reveal  the  fact 
that  fossils  or  the  remains  of  animals  and  plants  are  found  in  certain 
kinds  of  rocks  only.  They  are  not  found  in  lava,  because  'lava 
comes  from  volcanoes  and  rifts  in  the  earth's  crust,  as  a  red-hot, 
viscous  liquid,  which  cools  to  form  a  hard  rock.  No  animal  or  plant 
caught  in  a  lava  stream  will  leave  any  trace.  Furthermore,  fossils 
are  not  found  in  granite,  nor  in  ores  of  metals,  nor  in  certain  other  of 
the  common  rocks.  Many  rocks  are,  like  lava,  of  igneous  origin; 
others,  like  granite,  although  not  originally  in  the  melted  condition, 
have  been  so  heated  subsequent  to  their  formation,  that  any  traces  of 
animal  or  plant  remains  in  them  have  been  obliterated.  Fossils  are 
found  almost  exclusively  in  rocks  which  have  been  formed  by  the  slow 
deposition  in  water  of  sand,  clay,  mud,  or  lime.  The  sediment  which 
is  carried  into  a  lake  or  ocean  by  the  streams  opening  into  it  sinks 
slowly  to  the  bottom  of  the  lake  or  ocean  and  forms  there  a  layer 
which  gradually  hardens  under  pressure  to  become  rock.  This  is  called 
sedimentary  rock,  or  stratified  rock,  because  it  is  composed  of  sedi- 


EVIDENCES  FROM  PALAEONTOLOGY  65 

ment,  and  sediment  always  arranges  itself  in  layers  or  strata.  In 
'  sedimentary  or  stratified  rocks  fossils  are  found.  The  commonest 
rocks  of  this  sort  are  limestone,  sandstone,  and  shales.  Limestone  is 
formed  chiefly  of  carbonate  of  lime;  sandstone  is  cemented  sand,  and' 
shales,  or  slaty  rocks,  are  formed  chiefly  of  clay. 

''The  formation  of  sedimentary  rocks  has  been  going  on  since  land 
first  rose  from  the  level  of  the  sea;  for  water  has  always  been  wearing 
away  rock  and  carrying  it  as  sediment  into  rivers,  and  rivers  have 
always  been  carrying  the  w^orn-off  lime  and  sand  and  clay  downward 
to  lakes  and  oceans,  at  the  bottoms  of  which  the  particles  have  been 
piled  up  in  layers  and  have  formed  new  rock  strata.  But  geologists 
have  shown  that  in  the  course  of  the  earth's  history  there  have  been 
great  changes  in  the  position  and  extent  of  land  and  sea.  Sea  bottoms 
have  been  folded  or  upheaved  to  form  dry  land,  while  regions  once 
land  have  sunk  and  been  covered  by  lakes  and  seas.  Again,  through 
great  foldings  in  the  cooling  crust  of  the  earth,  which  resulted  in 
depression  at  one  point  and  elevation  at  another,  land  has  become 
ocean  and  ocean  land.  And  in  the  almost  unimaginable  period  of 
time  which  has  passed  since  the  earth  first  shrank  from  its  hypo- 
thetical condition  of  nebulous  vapor  to  be  a  ball  of  land  covered  with 
water,  such  changes  have  occurred  over  and  over  again.  They  have, 
however,  mostly  taken  place  slowly  and  gradually.  The  principal 
seat  of  great  change  is  in  the  regions  of  mountain  chains,  which,  in 
most  cases,  are  simply  the  remains  of  old  folds  or  wrinkles  in  the 
crust  of  the  earth. 

"When  an  aquatic  animal  dies,  it  sinks  to  the  bottom  of  the  lake 
or  ocean,  unless,  of  course,  its  flesh  is  eaten  by  some  other  animal. 
Even  then  its  hard  parts  will  probably  find  their  way  to  the  bottom. 
There  the  remains  will  soon  be  covered  by  the  always  dropping  sedi- 
ment. They  are  on  the  way  to  become  fossils.  Some  land  animals 
also  might,  after  death,  get  carried  by  a  river  to  the  lake  or  ocean, 
and  find  their  way  to  the  bottom,  where  they,  too,  will  become  fossils, 
or  they  may  die  on  the  banks  of  the  lake  or  ocean  and  their  bodies 
,  may  get  buried  in  the  soft  mud  of  the  shores.  Or,  again,  they  are 
often  trodden  in  the  mire  about  salt  springs  or  submerged  in  quick- 
sand. It  is  obvious  that  aquatic  animals  are  far  more  likely  to  be 
.  preserved  as  fossils  than  land  animals.  This  inference  is  strikingly 
proved  by  fossil  remains.  Of  all  the  thousands  and  thousands  of 
kinds  of  extinct  insects,  mostly  land  animals,  comparatively  few  speci- 
mens  are  known  as  fossils.     On  the  other  hand,  the  shell-bearing 


66        READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGEN^CS 

mollusks  and  crustaceans  are  represented  in  almost  all  rock  deposits 
which  contain  any  kind  of  fossil  remains." — Jordan  and  Kellogg/ 

[The  study  of  geology  teaches  us  that  the  earth's  outer  zones  have 
undergone  within  the  period  of  vertebrate  history  numerous  profound 
changes  which  in  general  we  may  term  climatic  changes.  There  have 
been  periods  of  continental  subsidence,  accompanied  by  ocean-floor 
elevations,  during  which  great  continental  plains  have  been  covered 
with  comparatively  shallow  seas.  The  marine  faunas  of  the  seas  have 
migrated  into  these  shallows  and  representatives  of  them  have  been 
buried  in  sediment.  When  the  reverse  change  has  occurred  and  the 
continental  plain  has  been  again  elevated,  the  sedimentation  of  the 
shallow-sea  period  forms  a  great  rocky  stratum  laden  with  marine 
fossils.  Between  periods  of  subsidence  millions  of  years  elapsed,  and 
therefore  a  break  in  the  continuity  of  the  entombed  fossils  is  to  be 
expected.  Discontinuity  between  the  fossil  faunas  in  adjacent  strata 
is  the  invariable  rule.  Were  it  not  for  this  periodicity  of  subsidence 
and  elevation  there  would  be  no  boundaries  between  consecutive 
geologic  strata. 

In  addition  to  the  methods  of  fossilization  mentioned,  a  few  others 
deserve  notice.  Many  animals  of  the  arid  plains  have  been  fossilized 
by  becoming  imbedded  in  dust  or  sand  drifts  which  have  piled  up 
against  rocky  outcrops  or  have  filled  in  dried-up  arroyos.  Some  very 
valuable  fossils  have  been  recovered  from  asphaltic  deposits  as  the 
result  of  animals  falling  into  liquid  or  semiliquid  lakes  or  pools  of 
asphalt. 

Not  only  are  external  organs  preserved  with  precision,  but  even 
delicate  internal  structures,  such  as  the  brains  or  the  viscera  of  verte- 
brates, have  been  found  in  such  a  perfectly  natural  shape  that  the 
comparative  anatomy  could  be  worked  out  with  confidence. 

On  the  whole,  then,  we  must  conclude  that  the  earlier, pessimism 
regarding  the  inadequacy  and  insufficiency  of  fossil  data  is  giving  way 
before  a  steadily  increasing  optimism,  due  to  the  very  rapid  advance 
in  technique  and  the  surprisingly  abundant  discoveries  of  the  modern 
palaeontologist.  The  more  enthusiastic  of  the  new  school  of  fossil- 
hunters  do  not  despair  of  ultimately  bringing  to  light  all  of  the  really 
essential  links  in  the  chain  of  evidence  necessary  to  place  the  evolution 
theory  beyond  the  reach  of  controversy. — Ed.] 

^  From  D.  S.  Jordan  and  V.  L.  Kellogg,  Evolution  and  Animal  Life  (copy- 
right 1907).    Used  by  special  permission  of  the  publishers,  D.  Appleton  &  Company. 


EVIDENCES  FROM  P.\LAEONTOLOGY  67 

ON   THE    LAPSE    OF   TIME   DURING   WHICH   EVOLUTION   IS   BELIEVED 

TO   HAVE   TAKEN   PLACE 

"Independently  of  our  not  finding  fossil  remains  of  such  infinitely 
numerous  connecting  links  [referring  to  the  objection  that  all  steps  in 
the  evolution  of  modern  types  should  be  revealed  in  the  fossils],  it 
may  be  objected  that  time  cannot  have  sufficed  for  so  great  an  amount 
of  organic  change,  all  changes  having  been  effected  slowly.  It  is 
hardly  possible  for  me  to  recall  to  the  reader  who  is  not  a  practical 
geologist,  the  facts  leading  the  mind  feebly  to  comprehend  the  lapse 
of  time.  He  w^ho  has  read  Sir  Charles  Lyell's  grand  work  on  the 
Principles  of  Geology^  which  the  future  historian  will  recognize  as 
having  produced  a  revolution  in  natural  science,  and  yet  does  not 
admit  how  vast  have  been  the  past  periods  of  time,  may  at  once  close 
this  volume.  Not  that  it  suffices  to  study  the  Principles  of  Geology, 
or  to  read  special  treatises  by  different  observers  on  separate  forma- 
tions, and  to  mark  how  each  author  attempts  to  give  an  inadequate 
idea  of  the  duration  of  each  formation,  or  even  of  each  stratum.  We 
can  best  gain  some  idea  of  past  time  by  knowing  the  agencies  at  work, 
and  learning  how  deeply  the  surface  of  the  land  has  been  denuded, 
and  how  much  sediment  has  been  deposited.  As  Lyell  has  well 
remarked,  the  extent  and  thickness  of  our  sedimentary  formations  are 
the  result  and  the  measure  of  the  denudation  which  the  earth's  crust 
has  elsewhere  undergone.  Therefore  a  man  should  examine  for  him- 
self the  great  piles  of  superimposed  strata,  and  watch  the  rivulets 
bringing  down  the  mud,  and  the  waves  wearing  away  the  sea-cliffs,  in 
order  to  comprehend  something  about  the  duration  of  past  time,  the 
monuments  of  which  we  see  all  around  us." — Charles  Darwin,  Origin 
of  Species. 

"In  1862,"  says  Schuchert,^  "the  physicist.  Lord  Kelvin  .... 
held  that  as  our  planet  was  continually  losing  energy  in  the  form  of 
heat,  the  globe  was  a  molten  mass  somewhere  between  20,000,000  and 
400,000,000  years  ago,  with  a  probabihty  of  this  state  occurring  about 
98,000,000  years  ago.  Finally  in  1897  he  concurred  in  Clarence  King's 
conclusion  that  the  globe  was  a  molten  mass  about  24,000,000  years  ago. 
Both  of  these  conclusions,  however,  were  wrought  out  under  the  Lap- 
lacian  hypothesis,  and  now  many  geologists  hold  that  the  earth  never 
was  molten.  While  geologists  have  not  been  able  to  fit  their  evidence 
into  so  short  a  time,  they  have  ever  since  been  trying  to  keep  their 

^  C.  Schuchert,  Texi-Book  of  Geology,  Part  II,  Historical  Geology  (191 5). 


68        READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 


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EVIDENCES  FROM  PALAEONTOLOGY  69 

estimates  within  the  bounds  of  Lord  Kelvin's  older  calculations.  Wal- 
cott,  in  1893,  on  the  basis  of  the  stratigraphic  record  and  the  known 
discharge  of  sediment  by  rivers,  concluded  that  70,000,000  years  had 
elapsed  since  sedimentation  began  in  the  Archeozoic.  Sir  Archibald 
Giekie  places  the  time  at  100,000,000  years,  and  most  geologists  have 
tried,  although  with  difficulty,  to  fit  the  record  within  these  estimates. 

^'  Since  the  discovery  of  radium,  all  of  the  calculations  previously 
made  have  been  set  aside  by  the  new  school  of  physicists,  and  now 
the  geologists  are  told  they  can  have  1,000,000,000  or  more  years  as 

the  time  since  the  earth  attained  its  present  diameter Even 

if  finally  it  shall  turn  out  that  the  physicists  have  to  reduce  their 
estimates  as  to  the  age  of  certain  minerals  and  rocks,  geologists 
nevertheless  appear  to  be  on  safer  ground  in  accepting  their  estimates 
than  those  based  either  on  sedimentation,  chemical  denudation,  or  loss 
of  heat  by  the  earth." 

[The  last  decade  has  seen  the  demise  of  the  outworn  objection  to 
evolution  based  on  the  idea  that  there  has  not  been  time  enough  for 
the  great  changes  that  are  believed  by  evolutionists  to  have  occurred  • 
Given  100,000,000  or  1,000,000,000  years  since  life  began,  we  can  then 
allow  1,000,000  years  for  each  important  change  to  arise  and  establish 
itself.  We  can  also  understand  why  it  is  that  so  little  change  can  be 
noted  in  the  majority  of  wild  animals  and  plants  within  the  historic 
period.  A  thousand  years  in  the  development  of  the  race  is  like  a 
second  in  the  development  of  an  individual  and,  though  no  one  can 
notice  any  change  in  a  growing  creature  in  a  second  or  a  minute,  very 
radical  changes  can  be  noted  in  an  hour  or  a  day  or  a  year.  We  cannot 
see  any  movement  in  an  hour  hand  of  a  clock,  but  it  moves  with 
certainty  around  the  dial  in  a  relatively  short  time.  There  is  there- 
fore no  shortage  of  time.  Evolution  may  have  been  infinitely  slow, 
but  time  has  been  infinitely  long.  The  accompanying  time  scale 
shows  the  lapse  of  time  and  the  distribution  in  time  of  the  main 
groups  of  animals  (Fig.  i). — Ed.] 

ON   THE   PRINCIPAL   GENERAL   FACTS   REVEALED   BY   A 
STUDY   OF   THE    FOSSILS 

[i.  None  of  the  animals  or  plants  of  the  past  are  identical  with 
those  of  the  present.  The  nearest  relationship  is  between  a  few  species 
of  the  past  and  some  living  species  which  have  been  placed  in  the  same 
families. 


70       READINGS  IX  E\'OLUTION,  GENETICS,  AND  EUGENICS 

2.  The  animals  and  plants  of  each  geologic  stratum  are  at  least 
generically  different  from  those  of  any  other  stratum,  though  belonging 
in  some  cases  to  the  same  families  or  orders. 

3.  The  animals  and  plants  of  the  oldest  (lowest)  geologic  strata 
represent  all  of  the  existing  phyla,  except  the  Chordata,  but  the 
representatives  of  the  various '  phyla  are  relatively  generalized  as 
compared  with  the  existing  types. 

4.  The  animals  and  plants  of  the  newest  (highest)  geologic  strata 
are  most  like  those  of  the  present  and  help  to  link  the  present  with 
the  past. 

5.  There  is,  in  general,  a  gradual  progression  toward  higher  types 
as  one  proceeds  from  the  lower  to  the  higher  strata. 

6.  Many  groups  of  animals  and  plants  reached  the  climax  of 
specialization  at  relatively  early  geologic  periods  and  became  extinct. 

7.  Only  the  less  specialized  relatives  of  the  most  highly  specialized 
types  survived  to  become  the  progenitors  of  the  modern  representa- 
tives of  their  group. 

8.  It  is  very  common  to  find  a  new  group  arising  near  the  end  of 
some  geologic  period  during  which  vast  climatic  changes  were  taking 
place.  Such  an  incipient  group  almost  regularly  becomes  the  domi- 
nant group  of  the  next  period,  because  it  developed  under  the 
changed  conditions  which  ushered  in  the  new,  period  and  was  therefore 
especially  favored  by  the  new  environment. 

9.  The  evolution  of  the  vertebrate  classes  is  more  satisfactorily 
shown  than  that  of  any  other  group,  probably  because  they  represent 
the  latest  phylum  to  evolve,  and  most  of  their  history  coincides  with 
the  period  within  which  fossils  are  known. 

10.  Most  of  the  invertebrate  phyla  had  already  undergone  more 
than  half  of  their  evolution  at  the  time  when  the  earliest  fossil  remains 
were  deposited. — Ed.] 

FOSSIL  PEDIGREES   OF   SOME   WELL-KNOWN   VERTEBRATES 

PEDIGREE    OF   THE    HORSE 

[Of  all  fossil  pedigrees  that  of  the  horse  is  most  often  mentioned  in 
evolutionary  literature.  The  main  facts  have  been  known  for  about 
forty  years,  and  there  is  a  rather  general  consensus  of  opinion  as  to  the 
history  as  a  whole.  It  appears  practically  certain  that  the  horse 
family  (Equidae)  arose  from  a  group  of  primitive  five-toed  ungulates 
or  hoofed  mammals  called  Condylarthra  that  lived  in  Eocene  times. 


EVIDENCES  FROM  PAI^AEONTOLOGY  71 

No  particular  member  of  this  extinct  group  has  been  found  that  fulfils 
all  the  requirements  of  a  primitive  horse  ancestor,  so  the  chances  are 
that  the  real  ancestral  condylarthran  has  not  been  discovered.' — Ed.] 

''The  course  of  their  [Equidae]  evolution,"  says  Dendy,'  ''has 
evidently  been  determined  by  the  development  of  extensive,  dry, 
grass-covered,  open  plains  on  the  American  continent.  In  adap- 
tation to  life  on  such  areas  structural  modification  has  proceeded 
chiefly  in  two  directions.  The  limbs  have  become  greatly  elongated 
and  the  foot  uplifted  from  the  ground,  and  thus  adapted  for  rapid 
flight  from  pursuing  enemies,  while  the  middle  digit  has  become  more 
and  more  important  and  the  others,  together  with  the  ulna  and  the 
fibula,  have  gradually  disappeared  or  become  reduced  to  mere  vestiges. 
At  the  same  time  the  grazing  mechanism  has  been  gradually  perfected. 
The  neck  and  head  have  become  elongated  so  that  the  animal  is  able 
to  reach  the  ground  without  bending  its  legs,  and  the  cheek  teeth  have 
acquired  complex  grinding  surfaces  and  have  greatly  increased  in 
length  to  compensate  for  the  increased  rate  of  wear.  As  in  so  many 
other  groups,  the  evolution  of  these  special  characters  has  been 
accompanied  by  gradual  increase  in  size.  Thus  EoJiippus,  of  Lower 
Eocene  times,  appears  to  have  been  not  more  than  eleven  inches  high 
at  the  shoulder,  while  existing  horses  measure  about  sixty-four  inches, 
and  the  numerous  intermediate  genera  for  the  rriost  part  show  a 
regular  progress  in  this  respect. 

"All  these  changes  have  taken  place  gradually,  and  a  beautiful 
series  of  intermediate  forms  indicating  the  different  stages  from  EoJiip- 
pus to  the  modern  horse  [Eqmis]  have  been  discovered.  The  sequence 
of  these  stages  in  geological  time  exactly  fits  in  with  the  theory  that 
each  one  has  been  derived  from  the  one  next  below  it  by  more  perfect 
adaptation  to  the  conditions  of  life.  Numerous  genera  have  been 
described,  but  it  is  not  necessary  to  mention  more  than  a  few." 

["The  first  indisputably  horselike  animal  appears  to  have  been 
Hyracotherium,''  of  the  Lower  Eocene  of  Europe.  Another  Lower 
Eocene  form  is  Eohippus,  which  lived  in  North  America,  probably 
having  migrated  across  from  Asia  by  the  Alaskan  land  connection 
which  was  in  existence  at  that  time.  In  Eohippus  the  fore  foot  had 
four  completely  developed  hoofed  digits  and  a  "thumb"  reduced  to 
a  splint  bone;  in  the  hind  foot  the  great  toe  had  entirely  disappeared 
and  the  Httle  toe  is  represented  by  a  vestigial  structure  or  splint  bone. 

^  Arthur  Dendy,  Outlines  of  Evolutionary  Biology  (D.  Appleton  &  Company, 
1916), 


72        READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

Then  came  in  succession  Orohippus,  of  the  Upper  Eocene,  Mesohippus 
of  the  Lower  Eocene,  Pliohippiis  of  the  Upper  Phocene,  and  finally 


Equus :  Qua- 
ternary and 
Recent. 


Pliohippus : 
Pliocene. 


*  Protohippus  : 
Lower  Plio- 
cene. 


Miohippus : 
Miocene. 


Mesohippus : 
Lower  Mio- 
cene. 


Orohippus 
Eocene. 


Fig.  2. — Feet  and  teeth  in  fossil  pedigree  of  the  horse.  {After  Marsh.) 
a,  Bones  of  the  fore  foot;  h,  bones  of  the  hind  foot;  c,  radius  and  ulna;  d,  fibula 
and  tibia;  e,  roots  of  a  tooth;  /  and  g,  crowns  of  upper  and  lower  teeth. 


Equus  of  the  Quaternary  and  Recent.     Other  genera  might  be  men- 
tioned, but  the  history  of  this  series  has  been  pictured  in  a  classic 


EVIDENCES  FROM  P.\LAEONTOLOGY 


73 


diagram  by  Marsh,  and  in  this  (Fig.  2)  the  reader  may  trace  upward 
from  Orohippus  to  Equus  the  steady  changes  in  fore  and  hind  feet, 
bones  of  the  forearm,  bones  of  the  lower  leg,  and  the  grinding  teeth 
of  upper  and  lower  jaws. 

So  definitely  and  clearly  has  the  horse  pedigree  been  worked  out 
that,  according  to  Dendy,  ''the  palaeontological  evidence  amounts  to 
a  clear  demonstration  of  the  evolution  of  the  horse  from  a  five-toed 
ancestor  along  the  lines  indicated  above." 

For  a  long  time  the  palaeontological  series  of  the  horse  was  un- 
rivaled by  other  vertebrate  types,  but  now  we  have  almost  equally 
complete  series  for  several  other  modern  types,  notably  the  camels 
and  the  elephants.  We  shall  present  herewith  accounts  of  the  pedi- 
gree of  the  camels  by  Professor  Scott,  and  that  of  the  elephants  by 
Professor  Shull.  And,  to  conclude  the  vertebrate  pedigrees,  we  shall 
present  in  the  next  chapter  that  of  man  as  given  by  Professor  Lull. 

In  extenuation  of  the  use  of  vertebrate  material  to  the  exclusion 
of  invertebrate,  the  present  writer  has  only  this  to  offer,  that  verte- 
brate material  is  more  intelligible  to  the  non-biological  reader  and  is 
more  in  his  own  field  of  knowledge  and  interest. — Ed.] 

PEDIGREE    OF    THE    CAMELS^ 
W.    B.    SCOTT 

There  remains  one  family  of  mammals  with  which  it  is  necessary 
to  deal  and  that  is  the  camel  tribe.  This  family  has  two  well-defined 
subdivisions,  the  camels  of  the  Old  World  and  the  llamas,  guanacos, 
etc.,  of  South  America.  For  a  very  long  time,  the  family  was  entirely 
confined  to  North  America  and  did  not  reach  its  present  homes  until 
the  Pliocene  epoch  of  the  Tertiary  period.  The  skeleton  of  a  Patago- 
nian  guanaco  may  be  taken  as  the  starting  point  of  our  inquiry.  In 
this  animal  the  third  incisor  and  the  canine  are  retained  in  the  upper 
jaw,  all  the  incisors  and  the  canine  in  the  lower.  The  anterior  two 
grinding  teeth  have  been  lost  and  the  others  are  moderately  high- 
crowned.  The  skull  is  broad  and  capacious  behind,  narrow  and 
tapering  in  front.  The  neck  is  long  and  its  vertebrae  very  curiously 
modified.  The  limbs  are  long  and  slender  and  have  undergone  nearly 
the  same  modifications  as  in  the  horses;  the  ulna  is  greatly  reduced, 
interrupted  in  the  middle  and  its  separated  portions  are  fused  with  the 
radius.     In  the  hind  leg  the  shaft  of  the  fibula  has  been  completely 

^  From  W.  B.  Scott,  The  Theory  of  Evolution  (copyright  1917)-  Used  by 
special  permission  of  the  publishers,  The  Macmillan  Company. 


74       READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

suppressed;  the  upper  end  fuses  with  the  tibia,  while  the  lower  remains 
as  a  small  separate  bone,  wedged  in  between  the  tibia  and  the  heel- 
bone.     The  feet  are  very  long  and  slender,  with  two  toes  in  each;    the 


Fig.  3. — Four  stages  in  the  evolution  of  the  cameline  skull.  A,  Protylopiis 
Upper  Eocene;  B,  Poebrotheriiim,  Lower  Eocene;  C,  Procamelus,  Upper  Miocene, 
Z>,  guanaco,  Recent.     {From  Scott.) 

long  bones  of  the  foot  are  co-ossified  to  form  a  '^  cannon-bone, "  the 
very  young  skeleton  showing  that  this  co-ossification  does  actually  take 
place.  The  toes  proper  are  free,  giving  the  "cloven  hoof,"  but  the 
hoofs  are  very  small  and  the  weight  is  carried  upon  a  soft,  thick  pad. 


EVIDENCES  FROM  PALAEONTOLOGY 


75 


IT        JH 


JF  M 


Fig.  4. — Four  stages  in  the  evolution  of  the  cameline  fore  foot.  A ,  Protylopus, 
Upper  Eocene;  B,  Poehrothcrium,  Lower  Eocene;  C,  Procamelus,  Upper  JMiocene; 
Z),  guanaco,  Recent.     {From  Scott.) 


76        READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

Were  there  time  enough  to  do  so,  we  might  trace  the  development 
of  this  family  backward,  step  by  step,  through  all  the  many  stages 
between  the  Pleistocene  and  the  Upper  Eocene  in  quite  as  unbroken 
sequence  and  in  as  full  detail  as  can  be  done  for  the  horses.  We  must, 
however,  pass  over  all  the  intermediate  steps  and  consider  the  ances- 
tral camels  of  the  Upper  Eocene.  These  were  very  little  animals, 
hardly  larger  than  a  jack  rabbit,  which  had  the  full  complement  of 
teeth,  44  in  total  number,  and  all  with  very  low  crowns.  The  limbs, 
and  especially  the  feet,  are  relatively  short,  the  ulna  is  complete  and 
separate,  as  is  also  the  fibula;  there  are  four  toes  in  each  foot,  though 
the  lateral  pair  of  the  hind  foot  are  extremely  slender,  and  there  is  no 
co-ossification  to  form  cannon-bones.  The  hoofs  are  well  developed, 
in  form  like  those  of  an  antelope,  so  that  there  can  have  been  no  pad. 
For  the  present,  the  line  cannot  be  carried  back  of  the  Upper  Eocene, 
the  probable  ancestors  from  the  middle  and  Lower  Eocene  being,  as 
yet,  represented  only  by  fragmentary  specimens. 

In  addition  to  this  main  stem  of  cameline  descent  which  resulted 
in  the  modern  species,  there  were  two  short-lived  side  branches  which 
should  be  mentioned.  One,  ending  in  the  Lower  Miocene,  was  the 
series  descriptively  called  '' gazelle-camels, "  small  animals  with  very 
long  and  slender  legs,  evidently  swift  runners.  The  other  series,  the 
so-called  "giraffe-camels,"  terminated  in  the  Upper  Miocene;  these 
were  browsers  and  display  an  increasing  stature,  especially  in  the 
length  of  the  neck  and  fore  limbs.  They  adapted  themselves  to  the 
growing  aridity  of  the  western  plains. 

EVOLUTION    OF    THE    ELEPHANTS^ 
A.    FRANKLIN   SHULL 

The  mastodon-elephant  series  shows  a  larger  number  of  obvious 
changes  than  most  of  the  other  series  named,  all  of  these  changes 
except  that  of  the  body  having  to  do  with  features  of  the  head. 
From  the  numerous  specimens  of  elephant-like  forms  available,  the 
following  are  selected  (following  Lull)  as  probably  representing  a 
direct  line  of  evolution:  Moeritheritim  from  the  Upper  Eocene  of 
Egypt;  Palaeomastodon  from  the  Lower  Oliogocene  of  Egypt,  also 
from  India;  Trilophodon  from  the  Miocene  of  Europe,  Africa,  and 
North  America;    Mastodon  from   the  Pliocene  and  Pleistocene    of 

^  From  A.  F.  Shull,  Principles  of  Animal  Biology  (copyright  1920).  Used  by 
special  permission  of  the  publishers.  The  McGraw-Hill  Book  Company. 


EVIDENCES  FROM  P.\LAEONTOLOGY 


77 


North  America,  Europe  and  Asia;  Stegodon  from  the  Phocene  of 
southern  Asia;  and  Elephas  from  the  Pleistocene  of  the  Americas, 
Europe,  and  Asia,  as  well  as  the  living  elephants  of  Asia  and  Africa. 


Fig.  5.— Evolution  of  head  and  molar  teeth  of  mastodons  and  elephants. 
A,  A',  Elephas,  Pleistocene;  B,  Stegodon,  Pliocene;  C,  C ,  Mastodon,  Pleistocene; 
D,  D',  Trilophodon,  Miocene;  E,  E' ,  Falaeomastodon,  Oligocene;  F,  F' ,  Moc- 
ritherium,  Eocene.     {From  Lull.) 


78       READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

A  study  of  Figure  5  in  connection  with  the  following  account  will  dis- 
close the  more  striking  steps  of  evolution.  These  forms  differed  from 
one  another  in  a  number  of  features,  but  the  differences  between  any 
member  of  the  series  and  the  one  that  precedes  or  that  which  follows 
were  so  small  that  the  series  is  obviously  a  continuous  one.  Moerithe- 
rium  was  very  different  from  the  modern  elephant,  but  the  inter- 
mediate forms  completely  bridged  the  gap.  The  series  exhibits  an 
enormous  increase  in  size  of  body,  changes  in  the  form  and  size  of 
the  teeth,  a  reduction  in  the  number  of  teeth,  an  alteration  in  the 
method  of  tooth  succession,  the  enlargement  of  certain  teeth  to 
become  tusks,  the  elongation  and  subsequent  shortening  of  the 
lower  jaw,  the  development  of  the  upper  lip  and  nose  into  a  proboscis, 
and  an  increase  in  the  height  of  the  skull  through  the  development 
of  large  cavities  in  the  substance  of  the  •  bone.  These  features  are 
described  in  the  several  forms  seriatim. 

Moeritherium. — The  earliest  animal  recognized  as  belonging  to 
the  elephant  series,  Moeritherium  by  name,  was  recovered  from  the 
late  Eocene  and  early  Oligocene  deposits  of  northern  Egypt. 
It  was  slightly  over  three  feet  in  height.  The  features  suggesting 
elephantine  affinities  are  the  high  posterior  portion  of  the  skull  (Fig. 
S,  F);  composed  of  somewhat  cancellate  bone,  that  is,  bone  containing 
open  spaces;  the  elongation  of  the  second  pair  of  incisors  in  each  jaw 
to  form  short  tusks;  the  indication  of  transverse  ridges  on  the  molar 
teeth  (Fig.  5,  F) ;  and  the  position  of  the  nasal  openings  some  distance 
back  of  the  tip  of  the  upper  jaw,  indicating  probably  a  prehensile 
upper  lip.  There  were  24  teeth,  and  the  neck  was  long  enough  to 
enable  the  animal  to  put  its  head  to  the  ground.  It  probably  fed 
upon  tender  shoots  and  swamp  vegetation. 

Palaeomastodon. — This  form  also  lived  in  Egypt,  but  has  recently 
been  found  in  India.  It  dates  from  early  Oligocene  time.  Palaeo- 
mastodon was  of  somewhat  larger  size  than  the  preceding  form,  the 
posterior  part  of  the  skull  was  distinctly  higher  (Fig.  5,  E') — with  a 
greater  development  of  cancellate  bone,  and  the  neck  was  somewhat 
shortened.  The  upper  incisors  of  the  second  pair  were  more  elongated 
as  tusks  and  bore  a  band  of  enamel  on  their  front  surfaces.  The  lower 
second  incisors  were  present,  but  not  enlarged.  All  other  incisors  and 
the  canines  had  disappeared.  The  molar  teeth  (£)  resembled  those 
of  Moeritherium  but  were  larger.  The  lower  jaw  was  considerably 
elongated,  and  the  total  number  of  teeth  was  still  high  (26).  The 
nasal  openings  had  receded  until  they  were  just  in  front  of  the  eyes, 


EVIDENCES  FROM  PALAEONTOLOCxY  yg 

• 
which  is  beheved   to  indicate  the    existence   of   a   short   proboscis 

extending  at  least  to  the  tips  of  the  tusks. 

Trilophodon. — Trilophodon,  a  great  migrant  and  consequently 
wide-spread  over  several  continents  as  stated  above,  exhibited  in 
several  respects  a  striking  advance  over  Palaeomastodon;  but  this 
advance  was  in  the  main  in  the  same  direction  as  was  indicated  by 
the  change  from  Moeriiherium  to  Palaeomastodon.  Trilophodon  was  a 
huge  animal,  nearly  as  large  as  modern  Indian  elephants.  The  tusks 
were  considerably  longer  (Fig.  5,  D')  and  still  bore  a  band  of  enamel. 
The  molar  teeth  were  large  and  greatly  reduced  in  number,  so 
that  only  two  were  present  at  any  one  time  on  each  side  of  each 
jaw.  The  surface  of  these  teeth  bore  a  somewhat  larger  number  of 
transverse  crests  (Fig.  5,  D)  than  were  present  in  the  earlier  forms. 
The  lower  jaw  was  enormously  elongated,  so  that  it  projected  as  far 
forward  as  the  tusks.  The  great  weight  of  the  lower  jaw  and  tusks 
was  associated  with  a  considerable  development  of  cancellate  bone 
in  the  skull,  to  which  the  supporting  muscles  of  the  neck  were 
attached.  Presumably  there  was  a  proboscis  which  extended  to  or 
beyond  the  tips  of  the  tusks  and  lower  jaw. 

Mastodon. — The  mastodons  on  the  whole  represent  a  line  of 
development  which  became  extinct;  but  in  their  incipient  stages  they 
appear  to  have  given  rise  to  the  succeeding  forms  leading  to  the 
elephants.  The  body  was  somewhat  larger  than  that  of  Trilophodon, 
being  about  the  size  of  the  Indian  elephant.  The  tusks  {C)  were 
much  elongated  (9  feet  or  more),  but  the  lower  jaw  was  greatly  short- 
ened and  the  lower  incisor  teeth  were  reduced  or  wanting.  The  molar 
teeth  (Fig.  5,  C)  were  scarcely  more  complex  than  earlier  forms,  and 
numbered  two  on  each  side  of  each  jaw.  They  were  still  crushing 
teeth,  and  the  food  must  have  been  tender  twigs  and  succulent  plants; 
indeed,  remains  of  such  objects  have  been  found  in  the  region  of  the 
stomach  of  the  fossil  mastodons. 

Stegodon.— This  animal  is  of  interest  chiefly  because  the  molar 
teeth  bore  five  or  six  well-defined  transverse  ridges  (Fig.  5,  ^).  These 
ridges  were  due  to  plates  of  enamel  extending  up  through  the  tooth, 
and  inclosing  a  substance  known  as  dentine.  Over  the  enamel  in  an 
unworn  tooth  was  a  thin  coat  of  a  third  substance  called  cement,  but 
there  was  not  much  of  this  substance  between  the  ridges.  In  the 
latter  respect  Stegodon  differed,  as  is  pointed  out  below,  from  the 
elephants  and  mammoths.  On  the  whole,  Stegodon  was  intermediate 
between  the  mastodons  and  elephants. 


8o        READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

Elephas. — In  this  genus  are  included  a  number  of  extinct  forms 
(the  mammoths)  from  three  or  four  continents,  and  the  Hving  ele- 
phants. The  extinct  forms,  though  called  mammoths,  were  not  large 
animals,  being  no  larger  than  the  Indian  elephant  of  today,  and  not 
so  large  as  the  living  African  species.  Some  of  the  features  of  the 
elephants ,  their  size,  the  short  neck,  the  long  proboscis,  and  the  heavy- 
tusks  are  matters  of  common  observation.  The  skull'  is  very  high 
and  short  (Fig.  5,  A').  The  height  is  due  chiefly  to  the  development 
of  cancellate  bone,  not  to  the  enlargement  of  the  brain,  which  is  still 
quite  small.  As  stated  above,  the  high  skull  affords  the  necessary 
leverage  for  the  muscles  that  support  the  weight  of  the  tusks.  The 
molar  teeth  are  distinctly  grinding  teeth  (Fig.  5,  A).  Each  tooth 
bears  a  number  of  transverse  ridges,  about  ten  in  the  African  elephant 
and  two  dozen  or  more  in  the  Indian  species.  These  ridges  are  worn 
down  by  the  chewing  of  harsh  food,  so  that  the  upper  surface  displays 
a  number  of  flattened  tubular  plates  of  enamel  inclosing  dentine  and 
bound  together  by  cement.  A  tooth  is  completely  worn  out  by  use, 
and  is  replaced  by  another.  The  method  of  replacement,  however, 
is  peculiar.  While  the  tusks  (incisors)  are  of  two  sets,  one  following 
the  other  like  milk  and  permanent  teeth  of  other  mammals,  the 
grinders  succeed  one  another  in  continuous  fashion.  There  are  never 
more  than  two  visible  grinders  on  each  side  of  each  jaw.  As  they 
wear  out  they  move  forward  in  the  jaw,  and  are  replaced  by  new  teeth 
appearing  behind.  New  molars  thus  enter  at  intervals  of  two  to  four 
years  in  young  elephants,  and  at  intervals  of  15  to  30  years  in  later 
life.  If  an  elephant  lives  long  enough  (60  years  or  more)  it  develops 
a  total  of  28  teeth,  including  tusks,  but  has  not  more  than  ten  (often 
less)  at  any  one  time. 

Correlated  with  the  nature  of  the  teeth  of  the  elephants  are  their 
food  and  chewing  habits.  Whereas  the  ancestral  forms  whose  molars 
bore  prominent  elevations  lived  on  twigs  and  tender  herbage  which 
they  crushed  in  mastication,  the  mammoths  with  their  flattened  tooth 
surfaces  devoured  grasses,  sedges,  and  other  harsh  vegetation  which 
they  ground  with  lateral  motion  of  the  teeth  upon  one  another.  In 
this  respect  modern  elephants  are  like  the  mammoths. 

In  the  changes  described  above  is  found  one  of  the  most  beautiful 
and  best  established  evolutionary  series  with  which  the  palaeontolo- 
gist is  acquainted.  Only  a  few  others  equal  or  approach  it  in  clearness 
and  completeness. 


CHAPTER*  VI 

THE  EVOLUTION  OF  MAN:    PALAEONTOLOGY^ 

Richard  Swann  Lull 

ORIGIN   OF  PRIMATES 

Stock. — There  is  but  little  doubt  that  two  important  orders  of 
modern  mammals,  the  Carnivora  and  the  Primates,  had  a  common 
origin,  diverging  mainly  along  lines  determined  by  a  dietary  contrast, 
as  the  former  have  become  more  strictly  flesh-eating  or  predaceous, 
the  latter  largely  fruit-eating  and  as  a  consequence  more  completely 
arboreal.  Back  of  each  group  lie  as  annectant  forms  the  Insectivora, 
not  perhaps  such  as  are  alive  to-day,  as  all  these  are  highly  specialized 
along  diverse  lines,  but  generalized  insectivores  possessing,  because 
of  their  primitiveness,  a  wider  range  of  potential  adaptation.  Mat- 
thew is  ''disposed  to  think  of  these,  our  distant  ancestors,  at  the  dawn 
of  the  Tertiary,  as  a  sort  of  hybrid  between  a  lemur  and  a  mongoose, 
rather  catholic  in  their  tastes,  living  among  and  partly  in  the  trees, 
with  sharp  nose,  bright  eyes,  and  a  shrewd  little  brain  behind  them, 
looking  out,  if  you  will,  from  a  perch  among  the  branches,  upon  a 
world  that  was  to  be  singularly  kind  to  them  and  their  descendants." 
Thus  we  can  define  the  stock  as  a  relatively  large-brained  arboreal 
insectivore,  of  primitive  but  adaptable  dentition,  and  especially  of 
progressive  mentality. 

Time. — The  time  of  primate  origin  must  have  been  not  later 
than  basal  Eocene,  as  primates,  clearly  definable  as  such,  are  found  in 
the  Lower  Eocene  rocks  of  both  Europe  and  North  America. 

Place. — The  simultaneous  appearance  of  the  primate  in  the 
Old  World  and  the  New  gives  rise  to  the  same  conclusions  as  to  their 
place  of  origin  and  their  migrations  thence  as  with  other  modernized 
mammals.  It  suffices  now  to  say  that  their  ancestral  home  was 
boreal  Holarctica,  probably  within  the  limits  of  the  present  continent 
of  Asia,  whence  they  migrated  southward  along  the  three  great 
continental  radii.  The  impelling  cause  of  this  migration  was  the 
increasing  northern  cold,  before  which  the  boreal  limitations  of  the 
tropical  forests  retreated,  carrying  with  them  the  primates  which,  in 

^  From  R.  S.  Lull,  Organic  Evolution  (copyright  191  ?)•  Used  by  special 
permission  of  the  publishers,  The  Macmillan  Company. 

81 


82        READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

general,  are  utterly  dependent  upon  such  an  environment  for  their 
sustenance. 

Geologic  record. — Primates  are  found  in  the  North  American 
sediments  from  Lower  to  Upper  Eocene  time,  when  they  became 
extinct.  Thus,  while  their  remains  constitute  a  relatively  large  per- 
centage of  the  total  fauna  of  the  Eocene,  primates  are  utterly  unknown 
on  this  continent  from  that  time  until  the  coming  of  man.  In  Europe 
the  record  is  similar  except  that  the  extinction  occurred  at  a  somewhat 
later  date,  the  Oligocene.  Furthermore,  they  reappear  in  Europe  in 
the  Lower  Miocene,  at  the  time  of  the  proboscidean  migration  out  of 
Africa,  whence  these  primates  may  also  have  come.  Their  second 
European  extinction  was  in  the  Upper  Pliocene  shortly  before  the  first 
appearance  of  mankind. 

But  in  southern  Asia,  Africa,  and  South  America  the  evolution  of 
primates  seems  to  have  been  continuous  since  the  first  great  southward 
migration.  The  evidence,  however,  is  not  so  much  the  historical 
documents  as  the  presence  of  primates  in  those  places  at  the  present 
time,  the  fossil  record  is  not  entirely  lacking  although  highly  incom- 
plete. The  South  American  monkeys  may  have  had  their  origin  in 
the  ancient  North  American  primates,  or  more  doubtfully,  the  stock 
may  have  come  by  way  of  Africa.  Scott  inclines  toward  the  latter 
view  although  he  says  the  evidence  is  by  no  means  conclusive. 

ORIGIN   OF   MAN 

Stock. — According  to  W.  K.  Gregory,  the  stock  from  which  man 
arose  was  some  big-brained  anthropoid  related  most  nearly  to  the 
chimpanzee-gorilla  group,  an  assumption  based  upon  anatomical 
evidences,  in  spite  of  wide  differences  in  habitus  and  consequent 
adaptation. 

Place. — Evidences  point  to  central  Asia  as  the  place  of  descent 
from  the  trees  of  the  human  precursor,  the  reasons  for  this  belief  being 
several.  First,  it  was  central  for  migrations  elsewhere;  Europe,  on 
the  other  hand,  where  the  most  conclusive,  in  fact  almost  the  exclusive 
evidence  for  fossil  man  is  found,  is  too  small  an  area  for  the  divergent 
evolution  of  the  several  human  species.  Second,  Asia  is  contiguous 
to  the  oldest  known  human  remains,  which,  as  we  shall  see,  were  found 
in  Java.  Third,  it  was  the  seat  of  the  oldest  civilizations,  not  only  of 
the  existing  nations  which,  like  the  Chinese,  trace  their  recorded 
history  back  to  a  hoary  antiquity,  but  of  nations  which  preceded  them 
by  thousands  of  years,  and  whose  records  have  not  yet  come  to  light. 


THE  EVOLUTION  OF  MAN  83 

This  antiquity  vastly  exceeds  that  of  the  nations  of  Europe  or  of  the 
Americans  or  of  Africa.  Fourth,  central  Asia  is  the  source  of  almost 
all  of  our  domestic  animals,  many  of  which  have  been  subjected  to 
human  will  and  control  for  thousands  of  years,  and  this  is  equally  true 
of  many  of  our  domestic  plants.  This  is  not  due  to  the  fact  that  man 
first  reached  civilization  in  Asia,  but  rather  that  he  chose  for  his  com- 
panions the  highest  and  best  of  their  several  evolutionary  lines,  and 
Asia  was  the  place  of  all  others  upon  earth  where  the  evolution  in 
general  of  organic  life  reached  its  highest  development  in  late  Cenozoic 
time  (Williston).  Fifth,  climatic  conditions  in  Asia  in  the  Miocene 
or  early  Pliocene  were  such  as  to  compel  the  descent  of  the  prehuman 
ancestor  from  the  trees,  a  step  which  was  absolutely  essential  to 
further  human  development. 

Impelling  cause. — We  look  for  a  geologic  cause  back  of  this  most 
momentous  crisis  in  the  evolution  of  humanity  and  we  find  it  in  conti- 
nental elevation  and  consequent  increasing  aridity  of  climate,  espe- 
cially to  the  northward  of  the  Himalayas.  With  this  increased  aridity 
and  tempering  of  tropical  heat  came  the  dwindling  of  the  forested 
areas  suitable  to  primate  occupancy.  Barrell  has  suggested  that  this 
diminution  left  residual  forests  comparable  to  the  diminishing  lakes 
and  ponds  of  the  Devonian,  which  upon  final  desiccation  compelled 
their  denizens  to  become  terrestrial  or  perish.  The  dwindling  of  the 
residual  forests  would  have  an  effect  upon  the  tree-dwellers  which  may 
be  expressed  in  precisely  the  same  words.  Once  upon  the  ground  the 
effect  upon  even  a  conservative  type — and  the  primates  in  general, 
where  constant  conditions  prevail,  are  slow  of  change — would  be  the 
rapid  acquisition  of  such  adaptations  as  were  necessary  to  insure  sur- 
vival under  the  new  conditions.  The  other  man-like  apes  had, 
unfortunately  for  their  further  evolution,  reached  a  region  where 
tropical  forests  continued  to  be  available  and  hence  have  retained  their 
arboreal  life  and  with  it  a  stagnation  of  progress.  The  result  has  been, 
at  any  rate  on  the  part  of  the  three  larger  forms,  a  degeneracy  from 
the  estate  of  their  common  ancestry  with  mankind;  the  gibbons  seem 
to  have  deteriorated  less,  while  terrestrial  man  has  risen  to  the  summit 
of  primate  evolution. 

Time. — The  time  of  the  descent  is  not  later  than  early  Pliocene 
nor  earHer  than  Miocene  time;  when  the  terrestrial  ape-man  became 
what  we  would  call  human  was  perhaps  later,  but  certainly  during  the 
Pliocene,  which  makes  the  age  of  man  as  such  measurable  in  terms  of 
hundreds  of  thousands  of  years! 


84       READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

Significance  of  the  descent  from  trees. — As  a  result  of  the  descent 
from  the  trees,  certain  definite  factors  were  called  into  play,  each  of 
which  had  its  effect  on  the  further  evolution.  Briefly  enumerated, 
these  are:  (i)  Assumption  of  the  erect  posture;  (2)  liberation  of  the 
hands  from  their  ancient  locomotor  function  to  become  organs  of  the 
mind;  (3)  loss  of  the  easily  obtainable  food  of  the  tropical  forests, 
necessitating  the  search  for  sustenance,  both  plant  and  animal,  and 
man  became  a  hunter;  (4)  need  of  clothing  with  increasing  inclemency 
of  the  weather,  especially  during  the  long  winters;  (5)  freedom  from 
climatic  restrictions — when  an  omnivorous  diet  and  clothing  were 
acquired  man  was  no  longer  limited  to  one  definite  habitat  and  the 
result  was  dispersal;  (6)  the  development  of  communal  life,  rendered 
possible  by  the  terrestrial  habitat.  Primates  are  at  best  gregarious, 
submitting,  as  in  the  gorilla,  to  the  leadership  of  the  strongest  male, 
but  it  is  only  by  communal  life  with  its  attendant  division  of  labor 
that  man  can  rise  above  the  level  of  utter  savagery. 

Evolutionary  changes. — -Human  evolutionary  changes  which  are 
recorded  are:  more  erect  posture,  shorter  arms,  perfection  of 
thumb  opposability,  reduction  of  muzzle  and  of  size  of  teeth,  loss 
of  jaw  power,  development  of  chin  prominence,  increase  in  skull 
capacity,  diminution  of  brow-ridges,  diminution  in  strength  of  zygo- 
matic or  temporal  arch,  increase  in  size  and  complexity  of  brain, 
especially  frontal  lobes,  development  of  articulate  speech. 

FOSSIL   MAN 

Fossil  remains  of  man  are  found  under  two  conditions,  in  river 
valley  deposits  and  in  limestone  caverns  which  served  first  as  a 
dwelling-place  and  later  as  a  sepulture.  Of  these  the  caverns 
have  been  by  far  the  most  productive,  but  they  contain  only  the 
remains  of  the  later  races,  as  the  caverns  according  to  Penck  did  not 
become  available  for  human  occupancy  before  middle  Pleistocene 
time. 

The  rarity  of  human  fossils  may  be  explained,  first,  by  the  various 
burial  customs  which  seldom  are  sufficiently  perfect  to  preclude  the 
possibility  of  alternate  wetting  and  drying  or  of  rapid  oxidation,  both 
of  which  are  prohibitive  of  fossilization.  If  man  lived  and  died  in  the 
forests  the  chances  for  his  fossilization,  in  common  with  other  forest 
creatures,  was  very  remote,  for  the  remains  of  such  are  almost  invari- 
ably destroyed  by  other  animals,  by  dampness,  or  by  fungi,  and  rarely 
attain  a  natural  burial  in  sediment.     If,  on  the  other  hand,  he  dwelt 


THE  EVOLUTION  OF  MAN  85 

in  the  open,  the  chances  of  so  shrewd  a  creature  being  caught  in 
the  flood  waters  and  thus  buried  in  sediment  were  not  very  great. 
However  we  account  for  it,  the  fact  remains  that  reUcs  of  ancient  man 
are  rare  and  are  valued  accordingly. 

In  North  America. — Repeated  instances  of  seemingly  ancient 
man  have  been  brought  to  light  in  North  America,  such  as  the  "  Cale- 
veras  skull"  of  the  California  gold-bearing  gravels,  which  was  satirized 
by  Bret  Harte;  the  Nebraska  'Xoess  man,"  and  those  of  the  Trenton 
gravels;  none  of  which,  with  the  possible  exception  of  the  last- men- 
tioned, has  proved  to  be  really  old  in  the  geologic  sense.  Indirect 
evidence  of  human  antiquity,  that  is,  the  association  of  North  Ameri- 
can man  with  animals  which  are  now  extinct,  while  very  rare,  has  been 
reported  in  at  least  two  highly  authentic  instances.  The  first  of  these 
was  at  Attica,  New  York,  and  is  attested  by  Doctor  John  M.  Clarke, 
the  New  York  state  geologist.  Four  feet  below  the  surface  of  the 
ground,  in  a  black  muck,  he  found  the  bones  of  the  mastodon  (Masto- 
don americajtus) ,  and  12  inches  below  this,  in  undisturbed  clay,  pieces 
of  pottery  and  thirty  fragments  of  charcoal.  The  charcoal  may  have 
been  of  natural  origin,  but  the  presence  of  the  pottery  seems  conclu- 
sive. The  other  instance  was  that  of  the  remains  of  a  herd  of  extinct 
bison  {Bison  antiquus)  found  near  Smoky  Hill  River,  Logan  County, 
Kansas,  and  thus  described  by  Professor  Williston:  An  "arrow-head 
was  found  underneath  the  right  scapula  of  the  largest  skeleton, 
embedded  in  the  matrix,  but  touching  the  bone  itself.     The  skeleton 

was  lying  upon  the  right  side The  bone  bed  when  cleared  off 

....  contained  the  skeletons  of  five  or  six  adult  animals,  and  two  or 
three  younger  ones,  together  with  a  foetal  skeleton  within  the  pelvis 
of  one  of  the  adult  skeletons.  The  animals  had  evidently  all  perished 
together,  during  the  winter.     There  was  no  possibility  of  the  accidental 

intrusion  of  the  arrow-head  in  the  place  where  found It  must 

have  been  within  the  body  of  the  animal  at  the  time  of  death,  or  have 
been  lying  on  the  surface  beneath  its  body." 

What  at  this  writing  is  claimed  to  be  another  genuine  case  of  such 
an  association,  this  time  of  the  actual  human  bones,  has  just  been 
announced  from  Florida.  This  find,  which  has  been  reported  by 
State  Geologist  Sellards,  was  made  at  Vero,  eastern  Florida,  in  1913. 
The  fossil  human  bones  are  from  two  incomplete  skeletons  and  are 
found  in  strata  which  also  contain  remains  of  the  following  extinct 
species:  Elephas  columbi,  Eqiius  leidyi,  a  fox,  a  deer,  the  ground-sloth, 
Megalonyx  jefersoni,  and  the  American  mastodon. 


86        READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

In  South  America. — A  number  of  finds  have  been  recorded  from 
South  America,  notably  by  the  late  Florentino  Ameghino  of  Buenos 
Aires,  who  contributed  so  largely  to  our  knowledge  of  South  American 
prehistoric  life.  An  expert  from  Washington,  Doctor  Ales  Hrdlicka, 
has  studied  with  the  utmost  care  the  locality  and  character  of  each  of 
these  finds  in  the  Western  World,  and  has  expressed  the  opinion  that 
none  is  of  an  antiquity  greater  than  that  of  the  pre-Columbian 
Indians. 

Further  evidence  lies  in  the  uniformity  of  type,  except  for  minor 
distinctions,  of  all  native  American  peoples.  There  is  no  such  racial 
differentiation  as  that  seen  in  the  Old  World,  and  the  argument  is  that 
there  has  not  been  time  for  such  a  deployment.  The  area  and  condi- 
tions as  an  adaptive  radiation  center  are  surely  ample. 

In  Africa. — The  only  African  relics  thus  far  reported  are  those 
of  prehistoric  cultures,  comparable  to  those  of  Southern  Europe,  in 
certain  caverns  of  the  Barbary  States.  There  has  also  been  reported 
from  Oldoway  ravine,  German  East  Africa,  a  human  skeleton  of 
undoubted  antiquity.  It  is  described,  however,  as  being  neither  a 
very  early  nor  a  primitive  type. 

In  Asia. — Asia  has  given  us  in  Pithecanthropus  the  oldest  known 
relic  of  the  Hominidae,  found  at  Trinil  in  the  island  of  Java.  Osborn 
says:  "It  is  possible  that  within  the  next  decade  one  or  more  of  the 
Tertiary  ancestors  of  man  may  be  discovered  in  northern  India  among 
the  foothills  known  as  the  SiwaHks.  Such  discoveries  have  been 
heralded,  but  none  have  thus  far  been  actually  made.  Yet  Asia  will 
probably  prove  to  be  the  center  of  the  human  race.  We  have  now 
discovered  in  southern  Asia  primitive  representatives  or  relatives  of 
the  four  existing  types  of  anthropoid  apes,  namely,  the  gibbon,  the 
orang,  the  chimpanzee,  and  the  gorilla,  and  since  the  extinct  Indian 
apes  are  related  to  those  of  Africa  and  of  Europe,  it  appears  probable 
that  southern  Asia  is  near  the  center  of  the  evolution  of  the  higher 
primates  and  that  we  may  look  there  for  the  ancestors  not  only  of 
prehuman  stages  like  the  Trinil  race  but  of  the  higher  and  truly 
human  types." 

In  Europe.— It  is  in  Europe,  however,  that  the  tale  of  human 
prehistory  is  the  most  complete,  not  only  through  the  happy  accident 
of  preserval,  but  because  it  has  been  much  more  thoroughly  explored 
than  has  the  Asiatic  evolutionary  center.  The  latter,  however,  holds 
the  greatest  hopes  for  future  exploration  since,  as  we  have  emphasized, 
Europe  is  too  small  to  be  an  adaptive  radiation  center  and  European 


THE  EVOLUTION  OF  MAN  87 

prehistoric   man   represents   waves   of   migration   from   the  greater 
continent. 

Nevertheless  the  European  record  has  enabled  us  to  name  and 
define  a  number  of  distinct  human  species,  and  here  the  record  of  the 
cultural  evolution  of  man  is  also  unusually  complete.  Hence  Euro- 
pean chronology  is  taken  as  a  standard  in  describing  discoveries  from 
any  portion  of  the  world. 

CHRONOLOGICAL  TABLE 

(Adapted  from  Osborn,  19 15) 

Postglacial  Time 25,000  years 

Upper  Palaeolithic  culture 
Cro-Magnon  man 

Fourth  Glacial  Stage  (Wiirm,  Wisconsin) 50,000  years 

Close  of  Lower  Palaeolithic  culture 
Neanderthal  man 

Third  Interglacial  Stage 150,000  years 

Beginning  of  Lower  Palaeolithic  culture 
Piltdown  and  pre-Neanderthaloid  men 
Third  Glacial  Stage  (Riss,  lUiftoian) 175,000  years 

Second  Interglacial  Stage 375,000  years 

Heidelberg  man 

Second  Glacial  Stage  (Mindel,  Kansas) 400,000  years 

First  Interglacial  Stage 475,000  years 

Pithecanthropus,  ape-man 

First  Glacial  Stage  (Giinz,  Nebraskan) 500,000  years 

Pithecanthropus. — The  Java  ape-man,  Pithecanthropus  erectus 
(Figs.  6  and  7,  A),  was  discovered  in  Trinil,. on  the  Solo  orBengawan 
River  in  central  Java,  in 
1894.  The  type  consists  of 
a  calvarium  or  skull  cap,  a 
left    thigh   bone,  and    two  /  1   / 

upper    molar    teeth.     The  /  ^    I  ^ 

skull  is  characterized  by  its  /^\      — ^^ ^~-— — ^       v 

limited  capacity,  about  two-        /        V — f—^^^^y^-^p    ^       \ 

thirds  that  of  man ;  and  by     if/\/rn[^T23I 

the  low  flat  forehead  and 

beetling  brows.     Hence  not 

only  was  the  brain  limited 

in    its    total   size,    but    this  I'^^'-  6.-Skull  of   Java  ape-man,  FUycan- 

.   „       ,  ^     ,  thropiis  erectus.     {From  Lull,  after  Dubois.) 

was  especially  true  of  the 

frontal  lobes,  which,  as  we  have  seen,  are  the  seat  of  the  higher  intel- 
lectual faculties.     Thus,  as  Osborn  says,  although  touch,  taste,  and 


88        READINGS  IN  EVOLUTION,   GENETICS,  AND  EUGENICS 


vision  were  well  developed  there  was  a  limited  faculty  for  profiting 
by  experience  and  accumulated  tradition.     The  femur  associated  with 

the  skull  is  remarkable  for  its 
length  and  slight  curvature  as 
compared  with  the  primitive 
Neanderthal  race  of  Europe 
and  indicates  a  creature  fully 
as  erect  and  nearly  as  tall  as  the 
average  European  of  today, 
the  height  being  estimated  at  5 
feet  7  inches  as  compared  with 
5  feet  3  inches  for  the  Nean- 
derthals and  5  feet  8  inches, 
the  average  height  of  modem 
males.  The  erect  posture  of 
course  implies  the  liberation 
of  the  hands  from  any  part  in 
the  locomotor  function.  The 
teeth  are  somewhat  ape-like, 
but  are  more  human  than  are 
those  of  the  gibbon,  and  the 
human  mode  of  mastication 
has  been  acquired.  Certain 
authorities  have  tried  to  prove 
that  Pithecanthropus  is  nothing 
but  a  large  gibbon,  but  the 
weight  of  authority  considers 
it  prehuman,  though  not  in 
the  line  of  direct  development 
into  humanity.  It  is  neverthe- 
less a  highly  important  transi- 
tional form. 

Associated  with  the  Pithe- 
cmUhropus  remains  are  those 
of  a  number  of  the  contem- 
porary animals  which  fix  the 
date  as  either  of  the  Upper  Pho- 
cene  or  lowermost  Pleistoceen 
period,  which  being  rendered 
in  terms  of  years  gives  an  esti- 
mated age  of  about  500,000! 


Fig.  7. — Jaws,  left  outer  aspect,  of  A, 
chimpanzee,  Pan,  sp.;  B,  fossil  chimpanzee, 
Pan  veins,  found  in  association  with  Pilt- 
down  man;  C,  Heidelberg  man,  Homo 
heidelbergensis;  D,  modern  man,  H.  sapiens. 
{From  Lnll,  after  Woodward.) 


THE  EVOLUTION  OF  MAN  89 

Heidelberg  man. —  Homo  heidelhergensis,  the  Heidelberg  man, 
represents  the  oldest  recorded  European  race,  geologically  speaking. 
The  type  was  discovered  in  1907  in  river  sands,  79  feet  below  the 
surface,  at  Mauer,  near  Heidelberg,  South  Germany.  The  relic 
consists  of  a  perfect  lower  jaw  with  the  dentition  (Fig.  7,  C).  The 
description  by  the  discoverer.  Doctor  Schoetensack,  follows  (from 
Osborn) : 

''The  mandible  shows  a  combination  of  features  never  before 
found  in  any  fossil  or  recent  man.  The  protrusion  of  the  lower  jaw 
just  below  the  front  teeth  (the  chin  prominence)  which  gives  shape  to 
the  human  chin  is  entirely  lacking.  Had  the  teeth  been  absent  it 
would  have  been  impossible  to  diagnose  it  as  human.  From  a  fragment 
of  the  symphysis  of  the  jaw  it  might  well  have  been  classed  as  some 
gorilla-like  anthropoid,  while  the  ascending  ramus  resembles  that  of 
some  large  variety  of  gibbon.  The  absolute  certainty  that  these 
remains  are  human  is  based  on  the  form  of  the  teeth — molars,  pre- 
molars, canines,  and  incisors  are  all  essentially  human  and  although 
somewhat  primitive  in  form,  show  no  trace  of  being  intermediate 
between  man  and  the  anthropoid  apes  but  rather  of  being  derived  from 
some  older  common  ancestor.  The  teeth,  however,  are  small  for  the 
jaw;  the  size  of  the  border  would  allow  for  the  development  of  much 
larger  teeth.  We  can  only  conclude  that  no  great  strain  was  put  on 
the  teeth,  and  therefore  the  powerful  development  of  the  bones 
of  the  jaw  was  not  designed  for  their  benefit.  The  conclusion  is  that 
the  jaw,  regarded  as  unquestionably  human  from  the  nature  of  the 
teeth,  ranks  not  far  from  the  point  of  separation  between  man  and  the 
anthropoid  apes.  In  comparison  with  the  jaws  of  the  Neanderthal 
races  ....  we  may  consider  the  Heidelberg  jaw  as  pre-Neander- 
thaloid;  it  is,  in  fact,  a  generalized  type." 

Associated  with  the  Heidelberg  jaw  is  an  extensive  warm-climate 
fauna:  straight-tusked  elephant  (E.  antiquus),  Etruscan  rhinoceros, 
primitive  horse,  bison,  wild  cattle  (urus),  bear,  lion,  and  so  on,  all  of 
which  aid  in  establishing  the  date  of  the  jaw  as  Second  Interglacial 
and  its  age,  conservatively  estimated,  at  from  300,000  to  375,000  years. 
The  cultural  evolution  of  Heidelberg  man  is  indicated  by  the  presence 
of  eoliths,  flint  implements  of  the  crudest  workmanship,  if  indeed  their 
apparent  fashioning  is  not  merely  the  result  of  use. 

Neanderthal  man. — The  original  specimen  of  the  Neanderthal 
man.  Homo  neanderthalensis  or  primigenius  (Figs.  8,  9,  10)  was  dis- 
covered in  1856  not  far  from  Diisseldorf  in  Rhenish  Prussia.  Here 
the  valley  of  the  Diissel  forms  the  deep  Neanderthal  ravine,  whose 


go       READINGS  IX  EVOLUTION,  GENETICS,  AND  EUGENICS 

limestone  walls  are  penetrated  by  caverns,  in  one  of  which  the  remains 
were'found.     What  was  doubtless  a  perfect  skeleton  at  the  time  of  its 


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discovery  was  so  injured  by  its  finders  that  only  a  portion  of  it,  which 
is  now  preserved  in  the  Provincial  Museum  at  Bonn,  was  saved.  "  This 
prophet  of  an  unknown  race  was  for  a  time  utterly  without  honor 


THE  EVOLUTION  OF  MAN 


91 


though  of  course  the  subject  of  a  most  heated  controversy,  being  con- 
sidered as  non-human,  or,  as  Virchow  beUeved,  owing  its  distinctive 
characters  to  disease.  The  sagacity  of  Huxley  threw  true  hght  upon 
the  problem,  though  it  was  not  until  the  mute  testimony  of  other 
representatives  of  the  race  (the  men  of  Spy)  was  offered  that  even 
Huxley's  masterful  conception  of  the  Neanderthal  characters  was 
taken  as  an  accepted  fact. 
Professor  Huxley's  descrip- 
tion of  the  Neanderthal 
type  is  classic.     He  says: 

''The  anatomical  char- 
acters of  the  skeletons  bear 
out  conclusions  which  are 
not  flattering  to  the  appear- 
ance of  the  owners.  They 
were  short  of  stature  but 
powerfully  built,  with 
strong,  curiously  curved 
thigh  bones,  the  lower  ends 
of  which  are  so  fashioned 
that  they  must  have  walked 
with  a  bend  at  the  knees. 


Fig.  9. — Neanderthaloid  skull  of  L 
Chapelle-aux-Saints  {Homo  ncandcrlhalcnsis 
{From  Lull,  after  Boide.) 


Their  long  depressed  skulls  had  very  strong  brow-ridges;  their  lower 
jaws,  of  brutal  depth  and  solidity,  sloped  away  from  the  teeth  down- 
wards and  backwards  in  consequence  of  the  absence  of  that  especially 
characteristic  feature  of  the  higher  type  of  man,  the  chin  prominence." 

Subsequently  several  more  specimens  have  come  to  light,  at  Spy 
in  Belgium,  at  Krapina  in  Croatia,  at  Le  Moustier,  La  Chapelle-aux- 
Saints  and  La  Ferrassie  in  France,  and  at  Gibraltar,  which,  while 
differing  in  various  details,  effectually  serve  to  establish  the  race,  whose 
main  characteristics  are:  Heavy,  overhanging  brows,  retreating  fore- 
head, long  upper  lip;  jaw  less  powerful  than  that  of  the  Heidelberg 
man  but  very  thick  and  massive;  chin  generally  strongly  receding  but 
in  process  of  forming;  dentition  extraordinarily  massive  in  the  La 
Chapelle  specimen,  whereas  in  those  of  Spy  the  teeth  are  small.  The 
skull  in  many  characteristics  is  nearer  to  the  anthropoids  than  to 
modern  man. 

The  brain  is  large  and  its  volume  is  surely  human,  but  the  pro- 
portions are  again  less  like  those  of  recent  man  than  like  the  anthro- 
poids.    The   chest  is  large  and  robust,   the  shoulders   broad,  and 


92        READINGS  IX  EVOLUTION,  GENETICS,  AND  EUGENICS 


the  hand  large,  but  the  fingers  are  relatively  short,  the  thumb  lacking 
the  range  of  movement  seen  in  modern  man.  The  knee  was  some- 
what bent,  the  leg  powerful,  with  a  short  shin  and  clumsy  foot,  clearly 

not  of  cursorial  adaptation.  The 
curve  of  the  bent  leg  was  correlated 
with  a  similar  curvature  of  the 
spine,  so  that  the  man  could  not 
stand  fully  erect,  as  he  lacked  the 
fourth  or  cervical  curvature  of 
Homo  sapiens.  The  average  stature 
was  5  feet  3  inches,  with  a  range 
from  4  feet  10.3  inches  to  5  feet 
5.2  inches,  partly  sex  differences. 
Neanderthal  man  lived  in  Eu- 
rope from  the  Third  Interglacial 
stage  through  the  Fourth  Glacial, 
a  duration  of  thousands  of  years, 
and  then  became  extinct,  from 
twenty  to  twenty-five  millenniums 
ago.  He  seems  to  have  been  an 
actual  lineal  successor  of  the  man 
of  Heidelberg,  but  was  throughout 
his  long  career  an  unprogressive 
static  race.  One  of  the  most 
remarkable  features  in  connection 
with  this  race,  however,  was  the 
very  reverent  way  in  which  the 
dead  were  buried,  with  an  abun- 
dance of  ornaments  and  finely 
worked  flints.  This  can  have  but  one  interpretation,  the  awakening 
within  this  ancient  type  of  the  instinctive  belief  in  immortality! 

Piltdown  m.an. — In  191 2  was  announced  the  discovery  of  a  very 
ancient  man  from  the  Thames  gravels  at  Piltdown,  Sussex,  England. 
Here  again  the  skull  was  injured  and  partly  lost,  so  that  the  question 
of  its  proper  restoration  has  been  the  subject  of  considerable  contro- 
versy. The  material  consists  of  portions  of  the  cranial  walls,  nasal 
bones,  a  canine  tooth,  and  part  of  a  lower  jaw.  The  brain-case  in  this 
instance  is  typically  human,  except  for  the  remarkably  thick  cranial 
walls.  The  forehead  is  high  and  lacks  the  superorbital  ridges  of 
Neanderthal  man  and  Pithecanthropus.     While  the  skull  is  of  com- 


FiG.  10. — Skeleton  of  Neanderthal 
man.  A ,  Homo  neanderthalensis,  com- 
pared with  that  of  a  living  native 
Australian;  B,  Homo  sapiens,  the  latter 
the  lowest  existing  race,  (From  Lull, 
after  Woodward.) 


THE  EVOLUTION  OF  MAN  93 

paratively  high  human  type,  the  associated  jaw  and  canine  tooth 
clearly  are  not,  and  some  difficulty  was  met  in  explaining  their  evolu- 
tionary discrepancy.  That  has  apparently  been  answered,  however, 
by  the  conclusion  that  the  association  of  the  material  is  purely  acci- 
dental and  that  the  jaw  not  only  does  not  belong  with  the  skull,  but 
that  it  is  not  even  human  but  is  that  of  a  fossil  chimpanzee.  That 
being  the  case,  there  seems  to  be  no  reason  for  the  exclusion  of  the 
Piltdown  man,  who  has  been  named  Eoanthropus  dawsoni,  from  the 
direct  line  of  human  ancestry.  The  specimen  is  not,  perhaps,  so  surely 
dated  as  are  those  of  the  other  European  races,  but  it  is  associated  with 
a  warm-climate  fauna  and  is  generally  considered  to  belong  to  the 
Third  Interglacial  stage — from  100,000  to  150,000  years  old,  and 
hence  vastly  more  ancient  than  the  more  primitive  Homo  neonder- 
thalensis.     (See  Fig.  "j,  B.) 

Cro-Magnon  man. — The  original  finds  of  the  men  of  the  Cro- 
Magnon  race.  Homo  sapiens,  were  made  at  Gower,  Wales,  and  at 
Aurignac,  France.  In  the  latter  place  seventeen  skeletons  came  to 
light  in  1852,  but  were  buried  in  the  village  cemetery  and  thus  lost  to 
science,  and  not  until  1868,  when  five  more  skeletons  were  discovered 
at  Cro-Magnon,  France,  was  the  race  established.  These  individuals, 
an  old  man,  two  young  men,  a  woman  and  a  child,  are  thus  the 
types  of  the  race.     This  magnificent  race  is  thus  characterized : 

Skull  large  but  narrow,  with  a  broad  face,  hence  disharmonic. 
Facial  angle  equalling  the  highest  type  of  Homo  sapiens.  Jaw  thick 
and  strong,  with  a  narrow  but  very  prominent  chin.  Forehead  high 
and  orbital  ridges  reduced.  Brain  not  only  of  high  type  but  very 
large,  that  of  the  women  exceeding  the  average  male  of  to-day. 

The  stature  of  the  old  man  was  6  feet  4.5  inches;  the  average  for 
males  being  6  feet  1.5  inches,  for  women  5  feet  5  inches,  a  great  dis- 
parity. The  lower  segments  of  the  limbs  were  long,  in  contrast  with 
the  Neanderthal  type,  hence  the  men  of  Cro-Magnon  were  swift- 
footed,  while  those  of  Neanderthal  were  slow.  Osbom  says:  ''The 
wide,  short  face,  the  extremely  prominent  cheekbones,  the  spread  of 
the  palate  and  a  tendency  of  the  upper  cutting  teeth  and  incisors  to 
project  forward,  and  the  narrow,  pointed  chin  recall  a  facial  type 
which  is  best  seen  to-day  in  tribes  living  in  Asia  to  the  north  and  to 
the  south  of  the  Himalayas.  As  regards  their  stature  the  Cr6-:Magnon 
race  recall  the  Sikhs  living  to  the  south  of  the  Himalayas.  In  the 
disharmonic  proportions  of  the  face,  that  is,  the  combination  of 
broad  cheekbones  and  narrow  skull,  they  resemble  the  Eskimo.     The 


94        READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

sum  of  the  Cro-jMagnon  characters  is  certainly  Asiatic  rather  than 
African,  whereas  in  the  Grimaldis  (of  which  specimens  have  been 
found  in  association  with  Cro-Magnons  at  the  Grotte  des  Enfants, 
Mentone)  the  sum  of  the  characters  is  decidedly  negroid  or  African." 

The  Cro-Magnons  again  show  by  their  elaborate  burial  customs 
how  old  and  well  founded  is  the  belief  in  life  after  death.  They  are 
supposed  to  be  the  people  who  left  on  the  walls  of  the  caverns  of  France 
and  Spain  the  marvelous  examples  of  Upper  Palaeolithic  art  of  which 
Professor  Osborn's  book  gives  so  adequate  a  description.  They 
lived  for  a  while  contemporaneously  with  the  men  of  Neanderthal  and 
may  have  contributed  somewhat  to  the  final  extinction  of  the  latter. 
In  the  course  of  time,  however,  they  too  declined,  although  to  this 
day  survivors  of  the  race  may  be  seen  in  Dordogne,  at  Landes,  near 
the  Garonne  in  Southern  France,  and  at  Lannion  in  Brittany.  Osborn 
says: 

The  decHne  of  the  Cro-Magnons,  with  their  artistic  culture, 
''may  have  been  par  tly  due  to  environmental  causes  and  the  abandon- 
ment of  their  vigorous  nomadic  mode  of  life,  or  it  may  be  that  they  had 

reached  the  end  of  a  long  cycle  of  psychic  development We 

know  as  a  parallel  that  in  the  history  of  many  civilized  races  a  period 
of  great  artistic  and  industrial  development  may  be  followed  by  a 
period  of  stagnation  and  decline  without  any  apparent  environmental 


cause." 


Europe  was  repopulated  after  Cro-Magnon  decline  by  later 
invaders  from  the  Asiatic  realm,  the  so-called  Mediterranean  narrow- 
headed  and  the  Alpine  'broad-headed  types,  etc.,  probably  differen- 
tiated in  Asia  in  early  Palaeolithic  times.  The  repopulation  took 
place  in  the  Upper  Palaeolithic. 

EVIDENCES   OF  HUMAN   ANTIQUITY 

Great  variation. — These,  briefly  summarized,  are,  first,  great 
variation.  If  man  is  monophyletic,  that  is,  derived  from  a  single 
prehuman  species,  and  there  is  no  reason  to  believe  otherwise,  he  must 
be  old,  for  while  the  adaptations  to  ground-dwelling  after  the  descent 
from  the  trees  were  doubtless  relatively  rapidly  acquired,  the  differen- 
tiation into  the  various  races,  due  perhaps  largely  to  climatic  influ- 
ences rather  than  to  any  notable  environmental  change,  must  have 
been  slowly  attained.  As  corroborative  evidence  we  have  but  to 
point  to  the  mural  paintings  on  Egyptian  monuments,  dating  back 


THE  EVOLUTION  OF  MAN  95 

several  thousand  years,  in  which  are  depicted  the  Ethiopian,  Caucasian, 
and  the  Hke,  which  are  in  some  instances  striking  Ukenesses  of  the 
present-day  Egyptians. 

Universal  distribution  is,  in  animals,  another  mark  of  antiquity: 
in  man,  it  is  probably  less  so  because  of  his  greater  intelligence. 
And  yet  before  transportation  had  become  a  science  man's  spread 
over  land  and  sea  was  extremely  slow. 

High  intelligence  as  compared  with  that  of  the  anthropoids  is  also 
a  mark  of  antiquity,  for  the  brain,  especially  the  type  of  brain  found 
in  the  higher  human  races,  must  have  been  very  slow  of  development. 
Our  study  of  fossil  man  shows  this. 

Communal  life,  division  of  labor  and  all  of  the  complicated 
interactions  which  it  brings  about,  and  the  development  of  law  and 
religions  all  have  taken  time.  When  we  realize  that  Babylonian  texts, 
twice  as  remote  as  the  patriarch  Abraham,  give  evidence  of  highly 
perfect  laws  and  of  a  civilization  which  must  have  antedated  their 
production  by  centuries,  we  gain  another  yet  more  emphatic  im- 
pression of  human  antiquity.  Add  to  all  this  the  palaeontological 
evidence  of  man's  association  with  various  genera  and  numerous 
successive  species  of  prehistoric  animals  of  which  he  alone  survives, 
and  the  evidence  is  complete. 

FUTURE    OF   HUMANITY 

Because  of  his  intelligence  and  communal  co-operation  man  is  no 
longer  subject  to  the  laws  which  govern  the  adaptation  of  animals 
to  their  environment.  Osborn's  law  of  adaptive  radiation,  which,  as 
we  have  seen,  applies  equally  well  to  the  insects,  reptiles,  and  mam- 
mals, fails  in  its  application  to  mankind;  and  yet  man  has  become  as 
thoroughly  adapted  to  speed,  flight,  to  the  fossorial  and  aquatic  as 
they;  but  his  adaptation  is  artificial  and  to  a  very  small  extent  only 
alTects  his  physical  frame,  while  theirs  is  natural  and  the  stamp  of 
environment  is  deeply  impressed  upon  the  organism. 

Man's  physical  evolution  has  virtually  ceased,  but  in  so  far  as  any 
change  is  being  effected,  it  is  largely  retrogressive.  Such  changes  are: 
Reduction  of  hair  and  teeth,  and  of  hand  skill;  and  dulling  of  the 
senses  of  sight,  smell,  and  hearing  upon  which  active  creatures  depend 
so  largely  for  safety.  That  sort  of  charity  which  fosters  the  physi- 
cally, mentally,  and  morally  feeble,  and  is  thus  contrary  to  the  law  of 
natural  selection,  must  also  in  the  long  run  have  an  adverse  effect  upon 
the  race. 


96        READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

Man  is  hardly  as  yet  subject  to  Malthus'  law,  for  while  he  is 
increasing  more  rapidly  than  any  other  animal,  owing  largely  to  the 
care  of  the  young  which  makes  the  expectation  of  life  of  the  new-born 
relatively  very  high,  his  migratory  ability,  but  above  all  his  intelli- 
gence, save  him  from  the  application  of  the  law.  A  single  new  dis- 
covery such  as  that  of  electricity  may  increase  his  food  supply  and 
other  life  necessities  several  fold.  His  future  evolution,  in  so  far  as 
it  is  progressive,  will  be  mental  and  spiritual  rather  than  physical,  and 
as  such  will  be  the  logical  conclusion  of  the  marvelous  results  of 
organic^evolution. 


CHAPTER  VII 

EVIDENCES  FROM  GEOGRAPHIC  DISTRIBUTION 

[Just  as  palaeontology  may  be  said  to  be  a  study  of  the  vertical 
distribution  (distribution  in  time)  of  organisms,  so  geographic  distribu- 
tion may  be  called  a  study  of  the  horizontal  distribution  of  organisms, 
on  the  earth's  surface  at  any  given  time  (spatial  distribution).  We  are 
chiefly  to  be  concerned  with  the  present  spatial  distribution  of  animal 
and  plant  species,  but  equally  interesting  studies  have  been  and  still 
may  be  made  of  the  horizontal  or  contemporaneous  existence  of 
extinct  forms.  Much  new  knowledge  has  been  gained  by  combining 
the  data  of  palaeontology  with  those  of  geographic  distribution.  In 
fact,  neither  field  can  be  studied  profitably  without  recourse  to  the 
other.  This  fact  was  clearly  perceived  by  J.  A.  Thomson  in  his  little 
manual  on  Evolution  when  he  combined  the  two  types  of  evidence  in 
one  chapter  under  the  title  "Evidences  of  Evolution  from  Explorer 
and  Palaeontologist." 

It  was  a  consideration  of  the  present  and  of  the  past  distribution 
of  Edentates  that  led  Charles  Darwin  to  his  first  clear  concept  of 
descent  with  modification.  In  his  voyage  on  the  "Beagle"  he  found 
that  present-day  Edentates  (armadillos,  sloths,  anteaters),  a  very 
peculiar  group  of  archaic  mammals,  are  practically  confined  to  South 
America.  When  he  also  found  that  the  only  fossil  Edentates,  resem- 
bling but  also  differing  from  the  existing  types,  are  also  confined  to 
South  America,  he  easily  arrived  at  the  only  inference  permitted  by 
the  facts:  that  the  present  Edentates  are  the  modified  descendants 
of  the  Edentates  of  the  past. 

The  following  quotations  from  both  an  older  and  a  recent  writer 
will  give  the  reader  a  clear  idea  of  the  ways  in  which  the  general  facts 
of  geographic  distribution  bear  witness  to  the  truth  of  the  evolutionary 
principle. — Ed.] 

"The  theory,"  says  Wallace,'  "which  we  may  now  take  as  estab- 
lished— that  all  the  existing  forms  of  life  have  been  derived  from  other 
forms  by  a  natural  process  of  descent  with  modification,  and  that  this 
same  process  has  been  in  action  during  past  geological  time — should 

^  From  A.  R.  Wallace,  Darwinism  (1889).  Used  by  special  permission  of  the 
publishers,  The  Macmillan  Company. 

97 


98        READINGS  IX  EVOLUTION,  GENETICS,  AND  EUGENICS 

enable  us  to  give  a  rational  account  not  only  of  the  peculiarities  of 
form  and  structure  presented  by  animals  and  plants,  but  also  of  their 
grouping  together  in  certain  areas,  and  their  general  distribution  over 
the  earth's  surface. 

"  In  the  absence  of  any  exact  knowledge  of  the  facts  of  distribution, 
a  student  of  the  theory  of  evolution  might  naturally  anticipate  that  all 
groups  of  allied  organisms  would  be  found  in  the  same  region,  and  that, 
as  he  travelled  farther  and  farther  from  any  given  centre,  the  forms 
of  life  would  differ  more  and  more  from  tho^e  which  prevailed  at  the 
starting-point,  till,  in  the  remotest  regions  to  which  he  could  penetrate, 
he  would  find  an  entirely  new  assemblage  of  animals  and  plants, 
altogether  unlike  those  with  which  he  was  familiar.  He  would  also 
anticipate  that  diversities  of  climate  would  always  be  associated  with  a 
corresponding  diversity  in  the  forms  of  life. 

"Now  these  anticipations  are  to  a  considerable  extent  justified. 
Remoteness  on  the  earth's  surface  is  usually  an  indication  of  diversity 
in  the  fauna  and  flora,  while  strongly  contrasted  climates  are  always 
accompanied  by  a  considerable  contrast  in  the  forms  of  life.  But 
this  correspondence  is  by  no  means  exact  or  proportionate,  and  the 
converse  propositions  are  often  quite  untrue.  Countries  which  are 
near  to  each  other  often  differ  radically  in  their  animal  and  vegetable 
productions;  while  similarity  of  climate,  together  with  moderate 
geographical  proximity,  are  often  accompanied  by  marked  diversi- 
ties in  the  prevailing  forms  of  life.  Again,  while  many  groups  of 
animals — genera,  families,  and  sometimes  even  orders — are  confined 
to  limited  regions,  most  of  the  families,  many  genera,  and  even 
some  species  are  found  in  every  part  of  the  earth.  An  enumeration 
of  a  few  of  these  anomalies  will  better  illustrate  the  nature  of  the 
problem  we  have  to  solve. 

"As  examples  of  extreme  diversity,  notwithstanding  geographical 
proximity,  we  may  adduce  Madagascar  and  Africa,  whose  animal  and 
vegetable  productions  are  far  less  alike  than  are  those  of  Great  Britain 
and  Japan  at  the  remotest  extremities  of  the  great  northern  continent; 
while  an  equal,  or  perhaps  even  a  still  greater,  diversity  exists  between 
Australia  and  New  Zealand.  On  the  other  hand,  Northern  Africa 
and  South  Europe,  though  separated  by  the  Mediterranean  Sea,  have 
faunas  and  floras  which  do  not  differ  from  each  other  more  than  do 
the  various  countries  of  Europe.  As  a  proof  that  similarity  of  climate 
and  general  adaptability  have  had  but  a  small  part  in  determining  the 
forms  of  life  in  each  country,  we  have  the  fact  of  the  enormous  increase 


EVIDENCES  FROM  GEOGRAPHIC  DISTRIBUTION  99 

of  rabbits  and  pigs  in  Australia  and  New  Zealand,  of  horses  and  cattle 
in  South  America,  and  of  the  common  sparrow  in  North  America, 
though  in  none  of  these  cases  are  the  animals  natives  of  the 
countries  in  which  they  thrive  so  well.  And  lastly,  in  illustration  of 
the  fact  that  allied  forms  are  not  always  found  in  adjacent  regions, 
we  have  the  tapirs,  which  are  found  only  on  opposite  sides  of  the 
globe,  in  tropical  America  and  the  Malayan  Islands;  the  camels  of 
the  Asiatic  deserts,  whose  nearest  allies  are  the  llamas  and  alpacas 
of  the  Andes;  and  the  marsupials,  only  found  in  Australia  and-  on 
the  opposite  side  of  the  globe  in  America.  Yet,  again,  although 
mammalia  may  be  said  to  be  universally  distributed  over  the  globe, 
being  found  abundantly  on  all  the  continents  and  on  a  great  many  of 
the  larger  islands,  yet  they  are  entirely  wanting  in  New  Zealand,  and 
in  a  considerable  number  of  other  islands  which  are,  nevertheless,  per- 
fectly able  to  support  them  when  introduced. 

''Now  most  of  these  difficulties  can  be  solved  by  means  of  well- 
known  geographical  and  geological  facts.  When  the  productions  of 
remote  countries  resemble  each  other,  there  is  almost  always  conti- 
Quity  of  land  with  similarity  of  climate  between  them.  When  adjacent 
countries  differ  greatly  in  their  productions,  we  find  them  separated  by 
a  sea  or  strait  whose  great  depth  is  an  indication  of  its  antiquity  or 
permanence.  When  a  group  of  animals  inhabits  two  countries  or 
regions  separated  by  wide  oceans,  it  is  found  that  in  past  geological 
times  the  same  group  was  much  more  widely  distributed,  and  may 
have  reached  the  countries  it  inhabits  from  an  intermediate  region 
in  which  it  is  now  extinct.  We  know,  also,  that  countries  now  united 
by  land  were  divided  by  arms  of  the  sea  at  a  not  very  remote  epoch, 
while  there  is  good  reason  to  believe  that  others  now  entirely  isolated 
by  a  broad  expanse  of  sea  were  formerly  united  and  formed  a  single  land 
area.  There  is  also  another  important  factor  to  be  taken  account  of 
in  considering  ho\y  animals  and  plants  have  acquired  their  present 
peculiarities  of  distribution, — changes  of  chmate.  We  know  that 
quite  recently  a  glacial  epoch  extended  over  much  of  what  are  now  the 
temperate  regions  of  the  northern' hemisphere,  and  that  consequently 
the  organisms  which  inhabit  those  parts  must  be,  comparatively 
speaking,  recent  immigrants  from  more  southern  lands.  But  it  is  a 
yet  more  important  fact  that,  down  to  middle  Tertiary  times  at  all 
events,  an  equable  temperate  climate,  with  a  luxuriant  vegetation, 
extended  to  far  within  the  Arctic  circle,  over  what  are  now  barren 
t  wastes,  covered  for  ten  months  of  the  year  with  snow  and  ice.    The 


100     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

Arctic  zone  has,  therefore,  been  in  past  times  capable  of  supporting 
almost  all  of  the  forms  of  life  of  our  temperate  regions;  and  we  must 
take  account  of  this  condition  of  things  whenever  we  have  to  specu- 
late on  the  possible  migration  of  organisms  between  the  old  and  new 
continents." 


"Many  of  the  facts  of  distribution,"  says  Shull,'  "are  capable  of 
interpretation  by  the  assumption  that  evolution  has  operated  with  the 
other  factors.  If  each  kind  of  animal  has  arisen  from  a  pre-existing 
kind,  then  each  group  of  related  animals  must  have  had  an  ancestral 
form,  and  if  the  component  parts  of  the  groups  are  widespread  the 
range  of  the  ancestral  form  may  be  considered  to  be  the  center  of 
dispersal  of  the  group.  The  facts  of  distribution  can  apparently  be 
interpreted  only  on  this  basis. 

"Accepting  evolution,  along  with  the  other  factors  which  can  be 
recognized,  the  method  of  distribution  is  generally  conceived  to  be  as 
follows.  The  ancestral  form  tends  to  spread  in  all  directions.  In 
some  directions  it  is  limited  by  unfavourable  conditions  either  through- 
out its  life  or  for  some  time.  In  other  directions  it  extends  its  range. 
Anywhere  within  its  range  new  types  of  individuals  may  arise  through 
the  process  of  evolution.  These  new  types  may  be  fitted  to  occupy 
new  regions,  and  if  they  are  formed  near  the  limits  of  the  range  they 
may  find  opportunity  to  spread  into  areas  which  are  inaccessible  to 
the  unaltered  members  of  the  species.  Thus  may  arise  recognizably 
distinct  forms  coincident  in  range  with  certain  environmental  condi- 
tions. If  particular  forms,  or  the  individuals  of  a  single  form,  are 
accidentally  (or  possibly  by  sporadic  migration)  transferred  across 
barriers  the  distribution  of  the  group  becomes  discontinuous.  If 
these  processes  have  been  going  on  for  a  long  time,  that  is,  if  the 
common  ancestors  of  a  group  of  forms  existed  long  ago,  the  range  may 
have  had  time  to  become  very  extensive,  or  its  discontinuity  very 
marked.  If,  contrariwise,  the  ancestors  were  comparatively  recent, 
the  range  is  likely  to  be  much  smaller.  For  this  reason,  groups  that 
have  diverged  far  enough  to  have  attained  the  rank  of  families  are  on 
the  whole  more  widespread  than  those  so  nearly  allied  as  to  be  con- 
sidered genera.  Should  the  environment  become  altered  within  a 
given  range,  the  occupying  form  might  be  driven  from  it  or  destroyed . 

^  From  A.  F.  Shull,  Principles  of  Animal  Biology  (copyright  1920).     Used  by 
special  permission  of  the  pubhshers,  The  McGraw-Hill  Book  Company. 


EVIDENCES  FROM  GEOGRAPHIC  DISTRIBUTION  loi 

If  the  environment  in  a  region  adjoining  a  range  should  change  in  a 
favourable  manner,  the  range  might  be  extended  at  that  point  without 
any  alteration  on  the  part  of  the  animals. 

''The. distribution  of  animals  is  inferred  to  be  in  harmony  with  this 
method,  which  involves,  it  will  be  noted,  the  factors  of  migration, 
evolution,  physiological  and  morphological  dependence  upon  the 
environment,  the  diversity  and  changeableness  of  the  earth's  surface, 
and  extinction;  and  in  this  manner  are  explained  the  differences  in 
geographical  position,  differences  in  size  of  range,  differences  in  the 
continuity  of  range  and  the  fact  that  ranges  are  at  first  continuous, 
differences  in  physical  and  biological  conditions  which  characterize 
the  ranges  of  different  forms,  and  the  geographical  proximity  of 
apparently  related  forms." 

SOME  OF  THE  MORE  SIGNIFICANT  FACTS  ABOUT  THE 
DISTRIBUTION  OF  ANIMALS 

THE    FAUNA   OF   OCEANIC   ISLANDS^ 

GEORGE    JOHN    ROMANES 

Turning  now  from  aquatic  organisms  to  terrestrial,  the  body  of 
facts  from  which  to  draw  is  so  large,  that  I  think  the  space  at  my  dis- 
posal may  be  best  utilized  by  confining  attention  to  a  single  division 
of  them — that,  namely,  which  is  furnished  by  the  zoological  study  of 
oceanic  islands. 

In  the  comparatively  limited — but  in  itself  extensive — class  of 
facts  thus  presented,  we  have  a  particularly  fair  and  cogent  test  as 
between  the  alternative  theories  of  evolution  and  creation.  For 
where  we  meet  with  a  volcanic  island,  hundreds  of  miles  from  any 
other  land,  and  rising  abruptly  from  an  ocean  of  enormous  depth,  we 
may  be  quite  sure  that  such  an  island  can  never  have  formed  part  of  a 
now  submerged  continent.  In  other  words,  we  may  be  quite  sure  that 
it  always  has  been  what  it  now  is — -an  oceanic  peak,  separated  from  all 
other  land  by  hundreds  of  miles  of  sea,  and  therefore  an  area  supplied 
by  nature  for  the  purpose,  as  it  were,  of  testing  the  rival  theories  of 
creation  and  evolution.  For,  let  us  ask,  upon  these  tiny  insular 
specks  of  land  what  kind  of  life  should  we  expect  to  find  ?  To  this 
question  the  theories  of  special  creation  and  of  gradual  evolution 
would  agree  in  giving  the  same  answer  up  to  a  certain  point.  For 
both  theories  would  agree  in  supposing  that  these  islands  would,  at  all 

^  From  G.  J.  Romanes,  Darwin  and  after  Darwin  (copyright  1892).  Used  by 
special  permission  of  The  Open  Court  Publishing  Company. 


I02      READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

events  in  large  part,  derive  their  inhabitants  from  accidental  or  occa- 
sional arrivals  of  wind-blown  or  water-floated  organisms  from  other 
countries — especially,  of  course,  from  the  countries  least  remote.  But, 
after  agreeing  upon  this  point,  the  two  theories  must  part  company  in 
their  anticipations.  The  special-creation  theory  can  have  no  reason 
to  suppose  that  a  small  volcanic  island  in  the  midst  of  a  great  ocean 
should  be  chosen  as  the  theatre  of  any  extraordinary  creative  activity, 
or  for  any  particularly  rich  manufacture  of  peculiar  species  to  be 
found  nowhere  else  in  the  world.  On  the  other  hand,  the  evolution 
theory  would  expect  to  find  that  such  habitats  are  stocked  with  more 
or  less  peculiar  species.  For  it  would  expect  that  when  any  organisms 
chanced  to  reach  a  wholly  isolated  refuge  of  this  kind,  their  descendants 
should  forthwith  have  started  upon  an  independent  course  of  evolu- 
tionary history.  Protected  from  intercrossing  with  any  members  of 
their  parent  species  elsewhere,  and  exposed  to  considerable  changes  in 
their  conditions  of  life,  it  would  indeed  be  fatal  to  the  general  theory 
of  evolution  if  these  descendants,  during  the  course  of  many  genera- 
tions, were  not  to  undergo  appreciable  change.  It  has  happened  on 
two  or  three  occasions  that  European  rats  have  been  accidentally 
imported  by  ships  upon  some  of  these  islands,  and  even  already  it  is 
observed  that  their  descendants  have  undergone  a  slight  change  of 
appearance,  so  as  to  constitute  them  what  naturalists  call  local 
varieties.  The  change,  of  course,  is  but  slight,  because  the  time 
allowed  for  it  has  been  so  short.  But  the  longer  the  time  that  a 
colony  of  a  species  is  thus  completely  isolated  under  changed  condi- 
tions of  life  the  greater,  according  to  the  evolution  theory,  should 
we  expect  the  change  to  become.  Therefore,  in  all  cases  where  we 
happen  to  know,  from  independent  evidence  of  a  geological  kind,  that 
an  oceanic  island  is  of  very  ancient  formation,  the  evolution  theory 
would  expect  to  encounter  a  great  wealth  of  peculiar  species.  On  ihe 
other  hand,  as  I  have  just  observed,  the  special-creation  theory  can 
have  no  reason  to  suppose  that  there  should  be  any  correlation 
between  the  age  of  an  oceanic  island  and  the  number  of  peculiar  species 
which  it  may  be  found  to  contain. 

Therefore,  having  considered  the  principles  of  geographical  distri- 
bution from  the  widest  or  most  general  point  of  view,  we  shall  pass  to 
the  opposite  extreme,  and  consider  exhaustively,  or  in  the  utmost 
possible  detail,  the  facts  of  such  distribution  where  the  conditions  are 
best  suited  to  this  purpose — that  is,  as  I  have  already  said,  upon 
oceanic  islands,  which  may  be  metaphorically  regarded  as  having  been 


EVIDENCES  FROM  GEOGRAPHIC  DISTRIBUTION  103 

formed  by  nature  for  the  particular  purpose  of  supplying  naturalists 
with  a  crucial  test  between  the  theories  of  creation  and  evolution. 
The  material  upon  which  my  analysis  is  to  be  based  will  be  derived 
from  the  most  recent  works  upon  geographical  distribution — espe- 
cially from  the  magnificent  contributions  to  this  department  of  science 
which  we  owe  to  the  labours  of  Mr.  Wallace.  Indeed,  all  that  follows 
may  be  regarded  as  a  condensed  filtrate  of  the  facts  which  he  has 
collected.  Even  as  thus  restricted,  however,  our  subject  matter 
would  be  too  extensive  to  be  dealt  with  on  the  present  occasion, 
were  we  to  attempt  an  exhaustive  analysis  of  the  floras  and  faunas 
of  all  oceanic  islands  upon  the  face  of  the  globe.  Therefore,  what  I 
propose  to  do  is  to  select  for  such  exhaustive  analysis  a  few  of  what 
may  be  termed  the  most  oceanic  of  oceanic  islands — that  is  to  say, 
those  oceanic  islands  which  are  most  widely  separated  from  main- 
lands, and  which,  therefore,  furnish  the  most  unquestionable  of 
test  cases  as  between  the  theories  of  special  creation  and  genetic 
descent. 

Azores. — A  group  of  volcanic  islands,  nine  in  number,  about  900 
miles  from  the  coast  of  Portugal,  and  surrounded  by  ocean  depths  of 
1,800  to  2,500  fathoms.  There  is  geological  evidence  that  the  origin 
of  the  group  dates  back  at  least  as  far  as  Miocene  times.  There  is  a 
total  absence  of  all  terrestrial  Vertebrata,  other  than  those  which  are 
known  to  have  been  introduced  by  man.  Flying  animals,  on  the 
other  hand,  are  abundant:  namely,  53  species  of  birds,  one  species  of 
bat,  a  few  species  of  butterflies,  moths  and  hymenoptera,  with  74 
species  of  indigenous  beetles.  All  these  animals  are  unmodified 
European  species,  with  the  exception  of  one  bird  and  many  of  the 
beetles.  Of  the  74  indigenous  species  of  the  latter,  36  are  not  found 
in  Europe;  but  19  are  natives  of  Madeira  or  the  Canaries,  and  3  are 
American,  doubtless  transplanted  by  drift-wood.  The  remaining  14 
species  occur  nowhere  else  in  the  world,  though  for  the  most  part 
they  are  allied  to  other  European  species.  There  are  69  known 
species  of  land-shells,  of  which  37  are  European,  and  32  peculiar, 
though  all  allied  to  European  forms.  Lastly,  there  are  480  known 
species  of  plants  of  which  40  are  peculiar,  though  allied  to  European 
species. , 

Bermudas. — A  small  volcanic  group  of  islands,  700  miles  from 
North  Carolina.  A  though  there  are  about  100  islands  in  the  group, 
their  total  area  does  not  exceed  50  square  miles.  The  group  is  sur- 
rounded by  water  varying  in  depth  from  2,500  to  3,800  fathoms.     The 


I04     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

only  terrestrial  Vertebrate  (unless  the  rats  and  mice  are  indigenous) 
is  a  lizard  allied  to  an  American  form,  but  specifically  distinct  from  it, 
and  therefore  a  solitary  species  which  does  not  occur  anywhere  else  in 
the  world.     None  of  the  birds  or  bats  are  peculiar,  any  more  than  in 
the  case  of  the  Azores;  but,  as  in  that  case,  a  large  percentage  of  the 
land-shells  are  so — namely,  at  least  one  quarter  of  the  whole.     Neither 
the  botany  nor  the  entomology  of  this  group  has  been  worked  out; 
but  I  have  said  enough  to  show  how  remarkably  parallel  are  the  cases 
of  these  two  volcanic  groups  of  islands  situated  in  different  hemispheres 
but  at  about  the  same  distance  from  large  continents.     In  both  there 
is  an  extraordinary  paucity  of  terrestrial  Vertebrata,  and  of  any 
peculiar  species  of  bird  or  beast.     On  the  other  hand,  there  is  in  both 
a  marvellous  wealth  of  peculiar  species  of  insects  and  land-shells. 
Now  these  correlations  are  all  abundantly  intelligible.     It  is  a  difficult 
matter  for  any  terrestrial  animal  to  cross  900,  or  even  700  miles  of 
ocean:  therefore  only  one  lizard  has  succeeded  in  doing  so  in  one  of  the 
two  parallel  cases;    and  living  cut  off  from  intercrossing  with  its 
parent  form,  the  descendants  of  that  lizard  have  become  modified  so  as 
to  constitute  a  peculiar  species.     But  it  is  more  easy  for  large  flying 
animals  to  cross  those  distances  of  ocean:  consequently,  there  is  only 
one  instance  of  a  peculiar  species  of  bird  or  bat — namely,  a  bull-finch 
in  the  Azores,  which,  being  a  small  land-bird,  is  not  hkely  ever  to  have 
had  any  other  visitors  from  its  original  parent  species  coming  over 
from  Europe  to  keep  up  the  original  breed.    Lastly,  it  is  very  much  more 
easy  for  insects  and  land-moUusca  to  be  conveyed  to  such  islands  by 
wind  and  floating  timber  than  it  is  for  terrestrial  mammals,  or  even 
than  it  is  for  small  birds  and  bats;  but  yet  such  means  of  transit  are 
not  sufficiently  sure  to  admit  of  much  recruiting  from  the  mainland 
for  the  purpose  of  keeping  up  the  specific  types.     Consequently,  the 
insects  and  the  land-shells  present  a  much  greater  proportion  of 
peculiar  species — namely,  one  half  and  one  fourth  of  the  land-shells  in 
the  one  case,  and  one  eighth  of  the  beetles  in  the  other.     All  these  cor- 
relations, I  say,  are  abundantly  inteUigible  on  the  theory  of  evolution; 
but  who  shall  explain,  on  the  opposite  theory,  why  orders  of  beetles 
and  land-mollusca  should  have  been  chosen  from  among  all  other 
animals  for  such  superabundant  creation  on  oceanic  islands,  so  that 
in  the  Azores  alone  we  find  no  less  than  32  of  the  one  and  14   of  the 
other  ?    And,  in  this  connection,  I  may  again  allude  to  the  peculiar 
species  of  beetles  in  the  island  of  Madeira,     Here  there  are  an  enor- 
mous number  of  peculiar  species,  though  they  are  nearly  all  related  to, 


EVIDENCES  FROM  GEOGRAPHIC  DISTRIBUTION  105 

or  included  under  the  same  genera,  as  beetles  on  the  neighboring  conti- 
nent. Now,  as  we  have  previously  seen,  no  less  than  200  of  these 
species  have  lost  the  use  of  their  wings.  Evolutionists  explain  this 
remarkable  fact  by  their  general  laws  of  degeneration  under  disuse, 
and  the  operation  of  natural  selection,  as  will  be  shown  later  on;  but 
it  is  not  so  easy  for'  special  creationists  to  explain  why  this  enormous 
number  of  peculiar  species  of  beetles  should  have  been  deposited  on 
Madeira,  all  aUied  to  beetles  on  the  nearest  continent,  and  nearly  all 
deprived  of  the  use  of  their  wings.  And  similarly,  of  course,  with  all 
the  peculiar  species  of  the  Bermudas  and  the  Azores.  For  who  will 
explain,  on  the  theory  of  independent  creation,  why  all  the  peculiar 
species,  both  of  animals  and  plants,  which  occur  on  the  Bermudas 
should  so  unmistakably  present  American  affinities,  while  those  which 
occur  on  the  Azores  no  less  unmistakably  present  European  affinities  ? 
But  to  proceed  to  other,  and  still  more  remarkable,  cases. 

The  Galapagos  Islands. — This  archipelago  is  of  volcanic  origin, 
situated  under  the  equator  between  500  and  600  miles  from  the  West 
Coast  of  South  America.  The  depth  of  the  ocean  around  them  varies 
from  2,000  to  3,000  fathoms  or  more.  This  group  is  of  peculiar 
interest,  from  the  fact  that  it  was  the  study  of  its  fauna  which  first 
suggested  to  Darwin's  mind  the  theory  of  evolution.  I  will,  therefore, 
begin  by  quoting  a  short  passage  from  his  writings  upon  the  zoological 
relations  of  this  particular  fauna. 

"Here  almost  every  product  of  the  land  and  of  the  water  bears  the 
unmistakable  stamp  of  the  American  continent.  There  are  twenty-six 
land  birds;  of  these,  twenty-one,  or  perhaps  twenty- three,  are  ranked 
as  distinct  species,  and  would  commonly  be  assumed  to  have  been  here 
created;  yet  the  close  affinity  of  most  of  these  birds  to  American 
species  is  manifest  in  every  character,  in  their  habits,  gestures,  and 
tones  of  voice.  So  it  is  with  the  other  animals,  and  with  a  large  pro- 
portion of  the  plants,  as  shown  by  Dr.  Hooker  in  his  admirable  Flora 
of  this  archipelago.  The  naturalist,  looking  at  the  inhabitants  of 
these  volcanic  islands  in  the  Pacific,  distant  several  hundred  miles 
from  the  continent,  feels  that  he  is  standing  on  American  land.  Why 
should  this  be  so  ?  Why  should  the  species  which  are  supposed  to 
have  been  created  in  the  Galapagos  Archipelago,  and  nowhere  else, 
bear  so  plainly  the  stamp  of  affinity  to  those  created  in  America  ? 
There  is  nothing  in  the  conditions  of  life,  in  the  geological  nature  of  the 
islands,  in  their  height  or  climate,  or  in  the  proportions  in  which  the 
several  classes  are  associated  together,  which  closely  resembles  the 


io6      READINGS  IX  EVOLUTION,  GENETICS,  AND  EUGENICS 

conditions  of  the  South  American  coast;  in  fact,  there  is  a  considerable 
dissimilarity  in  all  these  respects.  On  the  other  hand,  there  is  a  con- 
siderable degree  of  resemblance  in  the  volcanic  nature  of  the  soil,  in  the 
climate,  height,  and  size  of  the  islands,  between  the  Galapagos  and  Cape 
de  Verde  Archipelagoes;  but  what  an  entire  and  absolute  difference 
in  their  inhabitants!  The  inhabitants  of  the  Cape  de  Verde  Islands 
are  related  to  those  of  Africa,  like  those  of  the  Galapagos  to  America. 
Facts  such  as  these  admit  of  no  sort  of  explanation  on  the'  ordi- 
nary view  of  independent  creation;  whereas  in  the  view  here  main- 
tained it  is  obvious  that  the  Galapagos  Islands  would  be  likely  to 
receive  colonists  from  America,  and  the  Cape  de  Verde  Islands  from 
Africa;  such  colonists  would  be  liable  to  modification — the  principle  of 
inheritance  still  betraying  their  original  birthplace. " 

The  following  is  a  synopsis  of  the  fauna  and  flora  of  this  archi- 
pelago, so  far  as  at  present  known.  The  only  terrestrial  vertebrates 
are  two  peculiar  species  of  land- tortoise,  and  one  extinct  species;  five 
species  of  lizards,  all  peculiar — two  of  them  so  much  so  as  to  constitute 
a  peculiar  genus; — and  two  species  of  snakes,  both  closely  allied  to 
South  American  forms.  Of  birds  there  are  57  species,  of  which  no  less 
than  38  are  peculiar;  and  all  the  non-peculiar  species,  except  one, 
belong  to  aquatic  tribes.  The  true  land-birds  are  represented  by  31 
species,  of  which  all,  except  one,  are  peculiar;  while  more  than  half 
of  them  go  to  constitute  peculiar  genera.  Moreover,  while  they  are 
all  unquestionably  allied  to  South  American  forms,  they  present  a 
beautiful  series  of  gradations,  "from  perfect  identity  with  the  conti- 
nental species,  to  genera  so  distinct  that  it  is  difficult  to  determine  with 
what  forms  they  are  most  nearly  allied;  and  it  is  interesting  to  note 
that  this  diversity  bears  a  distinct  relation  to  the  probabilities  of, 
and  facilities  for,  migration  to  the  islands.  The  excessively  abund- 
ant rice-bird,  which  breeds  in  Canada,  and  swarms  over  the  whole 
United  States,  migrating  to  the  West  Indies  and  South  America, 
visiting  the  distant  Bermudas  almost  every  year,  and  extending  its 
range  as  far  as  Paraguay,  is  the  only  species  of  land-bird  which  remains 
completely  unchanged  in  the  Galapagos;  and  we  may  therefore  con- 
clude that  some  stragglers  of  the  migrating  host  reach  the  islands 
sufficiently  often  to  keep  up  the  purity  of  the  breed"  [Wallace]. 
Again,  of  the  thirty  peculiar  land-birds,  it  is  observable  that  the 
more  they  dift'er  from  any  other  species  or  genera  on  the  South 
American  continent,  the  more  certainly  are  they  found  to  have  their 
nearest  relations  among  those  South  American  forms  which  have  the 


EVIDENCES  FROM  GEOGRAPHIC  DISTRIBUTION  107 

more  restricted  range,  and  therefore  the  least  Hkely  to  have  found 
their  way  to  the  islands  with  any  frequency. 

The  insect  fauna  of  the  Galapagos  Islands  is  scanty,  and  chiefly 
composed  of  beetles.  These  number  35  species,  which  are  nearly  all 
peculiar,  and  in  some  cases  go  to  constitute  peculiar  genera.  The 
same  remarks  apply  to  the  twenty  species  of  land-shells.  Lastly,  of 
the  total  number  of  flowering  plants  (332  species)  more  than  one 
half  (174  species)  are  peculiar.  It  is  observable  in  the  case  of 
these  peculiar  species  of  plants — as  also  of  the  peculiar  species  of 
birds — that  many  of  them  are  restricted  to  single  islands.  It  is  also 
observable  that  with  regard  both  to  the  fauna  and  flora,  the  Galapagos 
Islands  as  a  whole  are  very  much  richer  in  peculiar  species  than  either 
the  Azores  or  Bermudas,  notwithstanding  that  both  the  latter  are 
considerably  more  remote  from  the  nearest  continents.  This  differ- 
ence, which  at  first  sight  appears  to  make  against  the  evolutionary 
interpretation,  really  tends  to  confirm  it.  For  the  Galapagos  Islands 
are  situated  in  a  calm  region  of  the  globe,  unvisited  by  those  periodic 
storms  and  hurricanes  which  sweep  over  the  North  Atlantic,  and  which 
every  year  convey  some  stragghng  birds,  insects,  seeds,  etc.,  to  the 
Azores  and  Bermudas.  Notwithstanding  their  somewhat  greater 
isolation  geographically,  therefore,  the  Azores  and  Bermudas  are 
really  less  isolated  biologically  than  are  the  Galapagos  Islands;  and 
hence  the  less  degree  of  peculiarity  on  the  part  of  their  endemic 
species.  But,  on  the  theory  of  special  creation,  it  is  impossible  to 
understand  why  there  should  be  any  such  correlation  between  the 
prevalence  of  gales  and  a  comparative  inertness  of  creative  activity. 
And,  as  we  have  seen,  it  is  equally  impossible  on  this  theory  to  under- 
stand why  there  should  be  a  further  correlation  between  the  degree 
of  peculiarity  on  the  part  of  the  isolated  species,  and  the  degree  in 
which  their  nearest  allies  on  the  mainland  are  there  confined  to  narrow 
ranges,  and  therefore  less  likely  to  keep  up  any  biological  communi- 
cation with  the  islands. 

St.  Helena. — 'A  small  volcanic  island,  ten  miles  long  by  eight 
wide,  situated  in  mid-ocean,  1,100  miles  from  Africa,  and  1,800  from 
South  America.  It  is  very  mountainous  and  rugged,  bounded  for  the 
most  part  by  precipices,  rising  from  ocean  depths  of  17,000  feet,  to  a 
height  above  the  sea-level  of  nearly  3,000.  When  first  discovered  it 
was  richly  clothed  with  forests;  but  these  were  all  destroyed  by  human 
agency  during  the  i6th,  17th,  and  i8th  centuries.  The  records  of  civili- 
zation present  no  more  lamentable  instance  of  this  kind  of  destruction. 


io8     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

From  a  merely  pecuniary  point  of  view  the  abolition  of  these  pri- 
meval forests  has  proved  an  irreparable  loss;  but  from  a  scientific 
point  of  view  the  loss  is  incalculable.  These  forests  served  to  harbour 
countless  forms  of  life,  which  extended  at  least  from  the  Miocene  age, 
and  which,  having  found  there  an  ocean  refuge,  survived  as  the  last 
remnants  of  a  remote  geological  epoch.  In  those  days,  as  Mr.  Wallace 
observes,  St.  Helena  must  have  formed  a  kind  of  natural  museum  or 
vivarium  of  archaic  species  of  all  classes,  the  interest  of  which  we  can 
now  only  surmise  from  the  few  remnants  of  those  remnants,  which  are 
still  left  among  the  more  inaccessible  portions  of  the  mountain  peaks 
and  crater  edges.     These  remnants  of  remnants  are  as  follows: 

There  is  a  total  absence  of  all  indigenous  mammals,  reptiles, 
fresh-water  fish,  and  true  land-birds.  There  is,  however,  a  species  of 
plover,  allied  to  one  in  South  Africa;  but  it  is  specifically  distinct,  and 
therefore  peculiar  to  the  island.  The  insect  life,  on  the  other  hand, 
is  abundant.  Of  beetles,  no  less  than  129  species  are  believed  to  be 
aboriginal,  and,  with  one  single  exception,  the  whole  number  are 
peculiar  to  the  island.  "But  in  addition  to  this  large  amount  of 
specific  peculiarity  (perhaps  unequalled  anywhere  else  in  the  world) 
the  beetles  of  this  island  are  remarkable  for  their  generic  isolation,  and 
for  the  altogether  exceptional  proportion  in  which  the  great  divisions  of 
the  order  are  represented.  The  species  belong  to  39  genera,  of  which 
no  less  than  25  are  peculiar  to  the  island;  and  many  of  these  are  such 
isolated  forms  that  it  is  impossible  to  find  their  allies  in  any  particular 
country"  [Wallace].  More  than  two-thirds  of  all  the  species  belong 
to  one  group  of  weevils — a  circumstance  which  serves  to  explain  the 
great  wealth  of  beetle-population,  the  weevils  being  beetles  which  live 
in  wood,  and  St.  Helena  having  been  originally  a  densely  wooded 
island.  This  circumstance  is  also  in  accordance  with  the  view  that  the 
peculiar  insect  fauna  has  been  in  large  part  evolved  from  ancestors 
which  reached  the  island  by  means  of  floating  timber;  for,  of  course, 
no  explanation  can  be  suggested  why  special  creation  of  this  highly 
peculiar  insect  fauna  should  have  run  so  disproportionately  into  the 
production  of  weevils.  About  two-thirds  of  the  whole  number  of 
beetles,  or  over  80  species,  show  no  close  affinity  with  any  existing 
insects,  while  the  remaining  third  have  some  relations,  though  often 
very  remote,  with  European  and  African  forms.  That  this  high 
degree  of  peculiarity  is  due  to  high  antiquity  is  further  indicated, 
according  to  our  theory,  by  the  large  number  of  species  which  some  of 
the   types  comprise.     Thus,   the  54  species  of  Cossonidae  may  be 


EVIDENCES  FROM  GEOGRAPHIC  DISTRIBUTION  109 

referred  to  three  types ;  the  1 1  species  of  Bemhidium  form  a  group  by 
themselves;  and  the  Heteromera  form  two  groups.  ''Now,  each  of 
these  types  may  well  be  descended  from  a  single  species,  which  origi- 
nally reached  the  island  from  some  other  land;  and  the  great  variety 
of  generic  and  specific  forms  into  which  some  of  them  have  diverged 
is  an  indication,  and  to  some  extent  a  measure,  of  the  remoteness  of 
their  origin"  [Wallace].  But,  on  the  counter-supposition  that  all  these 
128  peculiar  species  were  separately  created  to  occupy  this  particular 
island,  it  is  surely  unaccountable  that  they  should  thus  present 
such  an  arborescence  of  natural  affinities  amongst  themselves. 

Passing  over  the  rest  of  the  insect  fauna,  which  has  not  yet  been 
sufficiently  worked  out,  we  next  find  that  there  are  only  20  species  of 
indigenous  land-shells — which  is  not  surprising  when  we  remember  by 
what  enormous  reaches  of  ocean  the  land  is  surrounded.  Of  these  20 
species  no  less  than  13  have  become  extinct,  three  are  allied  to  Euro- 
pean species,  while  the  rest  are  so  highly  peculiar  as  to  have  no  near 
allies  in  any  other  part  of  the  globe.  So  that  the  land-shells  tell 
exactly  the  same  story  as  the  insects. 

Lastly,  the  plants  likewise  tell  the  same  story.  The  truly  indige- 
nous flowering  plants  are  about  50  in  number,  besides  26  ferns.  Forty 
of  the  former  and  ten  of  the  latter  are  peculiar  to  the  island,  and,  as 
Sir  Joseph  Hooker  tells  us,  "cannot  be  regarded  as  very  close  specific 
allies  of  any  other  plants  at  all."  Seventeen  of  them  belong  to  peculiar 
genera,  and  the  others  all  differ  so  markedly  as  species  from  their 
congeners,  that  not  one  comes  under  the  category  of  being  an  insular 
form  of  a  continental  species.  So  that  with  respect  to  its  plants,  no 
less  than  with  respect  to  its  animals,  we  find  that  the  island  of 
St.  Helena  constitutes  a  little  world  of  unique  species,  allied  among 
themselves,  but  diverging  so  much  from  all  other  known  forms  that 
in  many  cases  they  constitute  unique  genera. 

Sandwich  Islands. — These  are  an  extensive  group  of  islands, 
larger  than  any  we  have  hitherto  considered — the  largest  of  the  group 
being  about  the  size  of  Devonshire.  The  entire  archipelago  is  vol- 
canic, with  mountains  rising  to  a  height  of  nearly  14,000  feet.  The 
group  is  situated  in  the  middle  of  the  North  Pacific,  at  a  distance  of 
considerably  over  2,000  miles  from  any  other  land,  and  surrounded  by 
enormous  ocean  depths.  The  only  terrestrial  vertebrates  are  two 
lizards,  one  of  which  constitutes  a  peculiar  genus.  There  are  24 
aquatic  birds,  five  of  which  are  peculiar;  four  birds  of  prey,  two 
of  which  are  peculiar;   and  16  land-birds,  all  of  which  are  peculiar. 


no     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

Moreover,  these  i6  land-birds  constitute  no  less  than  lo  peculiar 
genera,  and  even  one  peculiar  family  of  five  genera.  This  is  an  amount 
of  peculiarity  far  exceeding  that  of  any  other  islands,  and,  of  course, 
corresponds  with  the  great  isolation  of  this  archipelago.  The  only 
other  animals  which  have  here  been  carefully  studied  are  the  land- 
shells,  and  these  tell  the  same  story  as  the  birds.  For  there  are  no  less 
than  400  species  which  are  all,  without  any  exception,  peculiar;  while 
about  three-quarters  of  them  go  to  constitute  peculiar  genera. 
Again,  of  the  plants,  620  species  are  believed  to  be  endemic;  and  of 
these  377  are  peculiar,  yielding  no  less  than  39  peculiar  genera. 

THE   FAUNA    OF   MADAGASCAR    AXD    NEW    ZEALAND^ 
A.    R.    WALLACE 

The  two  exceptions  just  referred  to  are-  Madagascar  and  New 
Zealand,  and  all  the  evidence  goes  to  show  that  in  these  cases  the  land 
connection  with  the  nearest  continental  area  was  very  remote  in  time. 
The  extraordinary  isolation  of  the  productions  of  Madagascar — almost 
all  the  most  characteristic  forms  of  mammalia,  birds,  and  reptiles  of 
Africa  being  absent  from  it — renders  it  certain  that  it  must  have  been 
separated  from  that  continent  very  early  in  the  Tertiary,  if  not  as  far 
back  as  the  latter  part  of  the  Secondary  period;  and  this  extreme 
antiquity  is  indicated  by  a  depth  of  considerably  more  than  a  thousand 
fathoms  in  the  Mozambique  Channel,  though  this  deep  portion  is  less 
than  a  hundred  miles  wide  between  the  Comoro  Islands  and  the  main- 
land. Madagascar  is  the  only  island  on  the  globe  with  a  fairly  rich 
mammalian  fauna  which  is  separated  from  a  continent  by  a  depth 
greater  than  a  thousand  fathoms;  and  no  other  island  presents  so 
many  peculiarities  in  these  animals,  or  has  preserved  so  many  lowly 
organised  and  archaic  forms.  The  exceptional  character  of  its  pro- 
ductions agrees  exactly  with  its  exceptional  isolation  by  means  of  a 
very  deep  arm  of  the  sea. 

New  Zealand  possesses  no  known  mammals  and  only  a  single 
species  of  batrachian;  but  its  geological  structure  is  perfectly  conti- 
nental. There  is  also  much  evidence  that  it  does  possess  one  mammal, 
although  no  specimens  have  been  yet  obtained.  Its  reptiles  and  birds 
are  highly  peculiar  and  more  numerous  than  in  any  truly  oceanic 
island.  Now  the  sea  which  directly  separates  New  Zealand  from 
Australia  is  more  than  2,000  fathoms  deep,  but  in  a  north-west  direc- 

^  From  A.  R.  Wallace,  Darwinism  (copyright  1889).  Used  by  special  permis- 
sion of  the  publishers,  The  Macmillan  Company. 


EVIDENCES  FROM  GEOGRAPHIC  DISTRIBUTION  iii 

tion  there  is  an  extensive  bank  under  i,ooo  fathoms,  extending  to  and 
including  Lord  Howe's  Island,  while  north  of  this  are  other  banks 
of  the  same  depth,  approaching  towards  a  submarine  extension  of 
Queensland  on  the  one  hand,  and  New  Caledonia  on  the  other,  and 
altogether  suggestive  of  a  land  union  with  Australia  at  some  very- 
remote  period.  Now  the  peculiar  relations  of  the  New  Zealand  fauna 
and  flora  with  those  of  Australia  and  of  the  tropical  Pacific  Islands  to 
the  northward  indicate  such  a  connection,  probably  during  the  Cre- 
taceous period;  and  here,  again,  we  have  the  exceptional  depth  of  the 
dividing  sea  and  the  form  of  the  ocean  bottom  according  well  with  the 
altogether  exceptional  isolation  of  New  Zealand,  an  isolation  which  has 
been  held  by  some  naturalists  to  be  great  enough  to  justify  its  claim 
to  be  one  of  the  primary  Zoological  Regions. 

THE   DISTRIBUTION    OF   MARSUPIALS' 
A.  R.  WALLACE 

This  singular  and  lowly  organised  type  of  mammals  constitutes 
almost  the  sole  representative  of  the  class  in  Australia  and  New 
Guinea,  while  it  is  entirely  unknown  in  Asia,  Africa,  or  Europe.  It 
reappears  in  America,  where  several  species  of  opossums  are  found; 
and  it  was  long  thought  necessary  to  postulate  a  direct  southern  con- 
nection of  these  distant  countries,  in  order  to  account  for  this  curious 
fact  of  distribution.  When,  however,  we  look  to  what  is  known  of  the 
geological  history  of  the  marsupials  the  difiiculty  vanishes.  In  the 
Upper  Eocene  deposits  of  Western  Europe  the  remains  of  several 
animals  closely  allied  to  the  American  opossums  have  been  found; 
and  as,  at  this  period,  a  very  mild  climate  prevailed  far  up  into  the 
arctic  regions,  there  is  no  difficulty  in  supposing  that  the  ancestors  of 
the  group  entered  America  from  Europe  or  Northern  Asia  during  early 
Tertiary  times. 

But  we  must  go  much  further  back  for  the  origin  of  the  Australian 
marsupials.  All  the  chief  types  of  the  higher  mammalia  were  in 
existence  in  the  Eocene,  if  not  in  the  preceding  Cretaceous  period, 
and  as  we  find  none  of  these  in  Australia,  that  country  must  have  been 
finally  separated  from  the  Asiatic  continent  during  the  Secondary  or 
Mesozoic  period.  Now  during  that  period,  in  the  Upper  and  the 
Lower  Oohte  and  in  the  still  older  Trias,  the  jaw-bones  of  numerous 
small  mammalia  have  been  found,  forming  eight  distinct  genera,  which 

'  From  A.  R.  Wallace,  Darwinism  (copyright  1889).  Used  by  special  per- 
mission of  the  publishers,  The  Macmillan  Company. 


112      READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

are  believed  to  have  been  either  marsupials  or  some  allied  lowly  forms. 
In  North  America  also,  in  beds  of  the  Jurassic  and  Triassic  formations, 
the  remains  of  an  equally  great  variety  of  these  small  mammalia  have 
been  discovered;  and  from  the  examination  of  more  than  sixty  speci- 
mens, belonging  to  at  least  six  distinct  genera.  Professor  Marsh  is  of 
the  opinion  that  they  represent  a  generalised  type,  from  which  the 
more  specialised  marsupials  and  insectivora  were  developed. 

From  the  fact  that  very  similar  mammals  occur  both  in  Europe 
and  America  at  corresponding  periods,  and  in  beds  which  represent  a 
long  succession  of  geological  time,  and  that  during  the  whole  of  this 
time  no  fragments  of  any  higher  forms  have  been  discovered,  it  seems 
probable  that  both  the  northern  continents  (or  the  larger  portion  of 
their  area)  were  then  inhabited  by  no  other  mammalia  than  these, 
with  perhaps  other  equally  low  types.  It  was,  probably,  not  later 
than  the  Jurassic  age  when  some  of  these  primitive  marsupials  were 
able  to  enter  Australia,  where  they  have  since  remained  almost  com- 
pletely isolated;  and,  being  free  from  the  competition  of  higher  forms, 
they  have  developed  into  the  great  variety  of  types  we  now  behold 
there.  These  occupy  the  place,  and  have  to  some  extent  acquired 
the  form  and  structure  of  distinct  orders  of  the  higher  mammals — the 
rodents,  the  insectivora,  and  the  carnivora — while  still  preserving  the 
essential  characteristics  and  lowly  organisation  of  the  marsupials. 
At  a  much  later  period — probably  in  late  Tertiary  times — the  ances- 
tors of  the  various  species  of  rats  and  mice  which  now  abound  in 
Australia,  and  which,  with  the  aerial  bats,  constitute  its  only  forms 
of  placental  mammals,  entered  the  country  from  some  of  the  adjacent 
islands.  For  this  purpose  a  land  connection  was  not  necessary,  as 
these  small  creatures  might  easily  be  conveyed  among  the  branches 
or  in  the  crevices  of  trees  uprooted  by  floods  and  carried  down  to  the 
sea,  and  then  floated  to  a  shore  many  miles  distant.  That  no  actual 
land  connection  with,  or  very  close  approximation  to,  an  Asiatic 
island  had  occurred  in  recent  times,  is  sufflciently  proved  by  the  fact 
that  no  squirrel,  pig,  civet,  or  other  widespread  mammal  of  the  Eastern 
hemisphere  has  been  able  to  reach  the  Australian  continent. 

THE    DISTRIBUTION    OF    BIRDS^ 
A.    R.   WALLACE 

These  vary  much  in  their  powers  of  flight,  and  their  capability  of 
traversing  wide  seas  and  oceans.     Many  swimming  and  wading  birds 

^  From  A.  R.  Wallace,  Darwinism  (copyright  1891).  Used  by  special  per- 
mission of  the  publishers,  The  Macmillan  Company. 


EVIDENCES  FROM  GEOGRAPHIC  DISTRIBUTION  113 

can  continue  long  on  the  wing,  fly  swiftly,  and  have,  besides,  the 
power  of  resting  safely  on  the  surface  of  the  water.  These  would 
hardly  be  limited  by  any  width  of  ocean,  except  for  the  need  of  food; 
and  many  of  them,  as  the  gulls,  petrels,  and  divers,  find  abundance  of 
food  on  the  surface  of  the  sea  itself.  These  groups  have  a  wide  distri- 
bution across  the  oceans;  while  waders — expecially  plovers,  sandpipers, 
snipes,  and  herons — are  equally  cosmopolitan,  travelling  along  the 
coasts  of  all  the  continents,  and  across  the  narrow  seas  which  separate 
them.  Many  of  these  birds  seem  unaffected  by  climate,  and  as  the 
organisms  on  which  they  feed  are  especially  abundant  on  arctic,  tem- 
perate, and  tropical  shores,  there  is  hardly  any  limit  to  the  range  even 
of  some  of  the  species. 

Land-birds  are  much  more  restricted  in  their  range,  owing  to  their 
usually  limited  powers  of  flight,  their  inability  to  rest  on  the  surface 
of  the  sea  or  to  obtain  food  from  it,  and  their  greater  specialisation, 
which  renders  them  less  able  to  maintain  themselves  in  the  new  coun- 
tries they  may  occasionally  reach.  Many  of  them  are  adapted  to  live 
only  in  woods,  or  in  marshes,  or  in  deserts;  they  need  particular  kinds 
of  food  or  a  limited  range  of  temperature;  and  they  are  adapted  to 
cope  only  with  the  special  enemies  or  the  particular  group  of  competi- 
tors among  which  they  have  been  developed.  Such  birds  as  these  may 
pass  again  and  again  to  a  new  country,  but  are  never  able  to  establish 
themselves  in  it;  and  it  is  this  organic  barrier,  as  it  is  termed,  rather 
than  any  physical  barrier,  which,  in  many  cases,  determines  the 
presence  of  a  species  in  one  area  and  its  absence  from  another.  We 
must  always  remember,  therefore,  that,  although  the  presence  of  a 
species  in  a  remote  oceanic  island  clearly  proves  that  its  ancestors 
must  at  one  time  have  found  their  way  there,  the  absence  of  a  species 
does  not  prove  the  contrary,  since  it  also  may  have  reached  the  island, 
but  have  been  unable  to  maintain  itself,  owing  to  the  inorganic  or 
organic  conditions  not  being  suitable  to  it.  This  general  principle 
applies  to  all  classes  of  organisms,  and  there  are  many  striking  illus- 
trations of  it.  In  the  Azores  there  are  eighteen  species  of  land-birds 
which  are  permanent  residents,  but  there  are  also  several  others  which 
reach  the  islands  almost  every  year  after  great  storms,  but  have  never 
been  able  to  establish  themselves.  In  Bermuda  the  facts  are  still  more 
striking,  since  there  are  only  ten  species  of  resident  birds,  while  no  less 
than  twenty  other  species  of  land-birds,  and  more  than  a  hundred 
species  of  waders  and  aquatics  are  frequent  visitors,  often  in  great 
numbers,  but  are  never  able  to  estabHsh  themselves. 


114     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

SUMMARY   OF   MAMMALIAN   DISPERSAL* 
HANS    GADOW 

Australia  as  the  earliest  great  mass  of  land  permanently  severed 
from  the  rest  is  in  almost  undisturbed  possession  of  the  lowest  mam- 
mals. It  is  the  sole  refuge  of  the  monotremes,  and  the  marsupials 
have  narrowly  escaped  a  similar  fate.  They  take  us  to  the  next 
independent  continent,  South  America.  This  had  three  chances,  or 
epochs,  of  being  stocked  with  mammals.  Within  the  Cretaceous  period 
it  seems  to  have  received  its  marsupial  stock  from  the  north,  the  pro- 
genitors of  all  modern  marsupials.  A  second  influx  during  the  early 
Tertiary  brought  edentates  and  rodents  as  its  first  Placentals  from 
Africa,  and  those  queer  Ungulates,  the  Toxodonts  and  Pyrotheria, 
unless  we  prefer  to  look  upon  these  Eocene  extinct  orders  as  truly 
aboriginal  to  South  America,  when  this  was  still  continuous  with  the 
ancient  Brazil- Afro-Indian  Gondwanaland.  The  third  and  last  inroad 
came  once  more  from  the  north,  when  with  the  close  of  the  Miocene 
permanent  connection  with  North  America  was  re-established.  This 
brought  the  modern  odd-toed  and  pair-toed  Ungulates,  with  dogs,  cats 
and  bears  in  their  wake,  and  lastly  man. 

There  remains  the  huge  North  World.  Eurasia  and  North  America 
have  always  formed  a  wide  circumpolar  ring,  which  repeatedly  broke 
and  joined  again.  Whatever  group  of  terrestrial  creatures  was 
developed  in  the  eastern,  Asiatic,  half,  was  sure  to  turn  up  in  the 
western,  and  vice  versa. 

Lastly,  the  mysterious  African  continent.  It  began  originally  as 
the  centre  of  the  ancient  equatorial  South  World;  it  has  lost  these  con- 
nections and  has  become  joined  to  the  northland,  after  many  vicissi- 
tudes. It  is  therefore  most  difficult  to  apportion  its  fauna  rightly; 
moreover  for  fossils  it  is  almost  a  blank,  except  Egypt.  It  must  have 
had  some  share  in  the  evolution  of  mammals,  like  edentates,  rodents, 
insectivores,  hyrax,  elephants,  sirenians  and  lemurs,  all  groups  with 
an  ancient  stamp.  But  what  share  it  had,  against  Eurasia,  in  the 
development  of  say  ungulates,  carnivores,  monkeys,  we  do  not  know. 
Not  much  is  likely  to  have  originated  in  Europe;  the  elephants,  rhinos, 
hippos,  lions  and  hyaenas  were  migrants  rather  from  than  to  Africa, 
rarely  across  some  Mediterranean  bridge,  usually  by  Asia  Minor. 

The  more  dominant  forms  of  our  present  fauna  have  originated,  to 
use  an  expression  of  Darwin's,  "in  the  larger  areas  and  more  efficient 

*  From  Hans  Gadow,  Wanderings  of  Animals  (1913),  Cambridge  University  Press 


EVIDENCES  FROM  GEOGRAPHIC  DISTRIBUTION  115 

workshops  of  the  north,"  and  the  balance  is  in  favour  of  Asia  as  the 
cradle  of  modern  mammals. 

Is  it  an  idle  dream  to  think  of  the  future  ?  A  survey  of  the  past 
reveals  the  vanishing  of  whole  faunas  from  extensive  countries,  which 
were  then  repeopled  by  other  forms  from  elsewhere.  What  has 
happened  before,  may  happen  in  times  to  come.  Countless  groups, 
once  flourishing,  are  no  more;  many  others  have  had  their  day  and  are 
now  on  the  decline,  whilst  others  are  flourishing  now,  are  even  in  the 
increase  and  seem  to  have  a  future  before  them.  Such  favoured 
assemblies  are  the  toads  and  frogs,  lizards  and  snakes,  Passerine  birds 
and  rodents,  mostly  the  small-sized  members  of  their  tribes;  the  days 
of  giants  are  past.  All  this  has  happened  in  the  natural  course  of 
events,  without  the  influence  of  man,  who  only  within  most  recent 
times  has  become  the  most  potent  and  destructive  factor  to  the  ancient 
faunas  of  the  world. 

SUMMARY  OF  THE  ARGUMENT  FOR  EVOLUTION  AS  BASED  ON 
GEOGRAPHIC   DISTRIBUTION 

[On  the  hypothesis  of  special  creation  or  on  any  other  hypothesis 
except  evolution  that  has  even  been  suggested,  the  extremely  intricate 
patchwork  of  animal  and  plant  distribution  remains  an  unsolvable 
picture  puzzle,  without  rhyme  or  reason.  When  this  puzzle  is  attacked 
with  the  aid  of  the  evolutionary  idea,  the  key  to  the  whole  maze  is 
furnished  and  the  difficulties  clear  up  with  remarkable  ease.  The 
whole  hodgepodge  makes  sense  and  we  can  understand  many  pre- 
viously irreconcilable  facts.  In  no  field  does  the  working  hypothesis 
of  evolution  work  to  such  advantage  as  in  this  field. 

On  the  basis  that  a  species  arises  at  one  place,  spreads  out  over 
large  areas,  becoming  modified  as  it  goes,  that  new  species  are  formed 
from  old  through  modification  after  isolation  from  the  parent-stock, 
how  do  the  facts  of  distribution  look  when  examined  in  detail  ? 

1.  Cosmopolitan  groups,  those  with  the  widest  distribution,  are 
those  to  whom  no  barriers  are  sufficient  to  check  migration,  e.g., 
strong  fliers,  Man,  earthworms  carried  by  Man. 

2.  Restricted  groups  are  usually  those  to  which  barriers  are 
readily  set  up  and  are  frequently  the  last  remnants  of  a  formerly 
successful  fauna  or  flora,  which  continue  to  survive  only  in  some 
restricted  area  where  the  conditions  are  rather  more  favorable  than 
elsewhere. 


Ii6      READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

3.  The  study  of  the  distribution  of  species  belonging  to  a  single 
genus  reveals  that  the  more  primitive  or  generalized  species  occupy  a 
central  position  and  the  most  specialized  species  are  at  the  outer 
boundaries  of  the  distributional  area. 

4.  The  faunas  and  floras  of  continental  islands  are  just  what  we 
should  expect  on  the  basis  that  there  was  at  one  time  a  land  connection 
with  the  nearest  continent;  that  at  this  time  the  faunas  and  floras  were 
the  same  on  both  island  and  continent;  that,  later,  the  continent  and 
island  were  separated  by  an  impassable  barrier  of  ocean;  and  that  the 
inhabitants  of  the  two  bodies  evolved  separately. 

5.  The  faunas  and  floras  of  oceanic  islands  are  like  those  of  the 
nearest  mainland  and  are  of  those  types,  for  the  most  part,  that  might 
most  readily  have  been  blown  or  carried  on  floating  debris. 

6.  The  conclusions  arrived  at  by  students  of  geographic  distribu- 
tion, past  and  present,  as  to  the  existence  of  former  land  connections, 
now  broken,  are  borne  out  by  the  independent  findings  of  geologists 
and  geographers. — Ed.] 


CHAPTER  VIII 
EVIDENCES  FROM  CLASSIFICATION 

THE  PRINCIPLES  OF  CLASSIFICATION^ 
A.    F.    SHULL 

The  International  Code. — Some  of  the  essential  features  of  the 
International  Code  are  as  follows.  The  first  name  proposed  for  a 
genus  or  species  prevails  on  the  condition  that  it  was  published  and 
accompanied  by  an  adequate  description,  definite  or  indication,  and 
that  the  author  has  applied  the  principles  of  binomial  nomenclature. 
This  is  the  so-called  law  of  priority.  The  tenth  edition  of  the  Sytema 
Naturae  of  Linnaeus  is  the  basis  of  the  nomenclature.  The  author  of 
a  genus  or  species  is  the  person  who  first  pubhshes  the  same  in  connec- 
tion with  a  definition,  indication  or  description,  and  his  name  in  full 
or  abbreviated  is  given  with  the  name;  thus,  Bascanian  anthonyi 
Stejneger.  In  citations  the  generic  name  of  an  animal  is  written  with 
a  capital  letter,  the  specific  and  subspecific  name  without  initial 
capital  letter.  The  name  of  the  author  follows  the  specific  name 
(or  subspecific  name  if  there  is  one)  without  intervening  punctuation. 
If  a  species  is  transferred  to  a  genus  other  than  the  one  under  which 
it  was  first  described,  or  if  the  name  of  a  genus  is  changed,  the  author's 
name  is  included  in  parentheses.  For  example,  Bascanion  anthonyi 
Stejneger  should  now  be  written  Coluber  anthonyi  (Stejneger),  the  ge- 
neric name  of  this  snake  having  been  changed.  One  species  constitutes 
the  type  of  the  genus;  that  is,  it  is  formally  designated  as  typical  of 
the  genus.  One  genus  constitutes  the  type  of  the  subfamily  (when  a 
subfamily  exists),  and  one  genus  forms  the  type  of  the  family.  The 
type  is  indicated  by  the  describer  or  if  not  indicated  by  him  is  fixed 
by  another  author.  The  name  of  a  subfamily  is  formed  by  adding 
the  ending  -inae,  and  the  name  of  a  family  by  adding  -idae  to  the  root 
of  the  name  of  the  type  genus.  For  example,  Colubrinae  and  Colubri- 
dae  are  the  subfamily  and  family  of  snakes  of  which  Coluber  is  the 
type  genus. 

The  basis  of  classification. — Early  systematists  largely  employed 
superficial  characters  to  differentiate  and  classify  animals,  and  their 

'  From  A.  F.  ShuU,  Principles  of  Animal  Biology  (copyright  1920).  Used  by 
special  permission  of  The  McGraw-Hill  Book  Company, 

117 


Ii8     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

classifications  were  thus  largely  artificial  and  served  principally  as 
convenient  methods  of  arrangement,  description  and  cataloging. 
Since  the  time  of  the  development  of  the  theory  of  descent  with 
modifications  by  Lamarck  (1809)  and  Darwin  (1859),  there  has  been 
an  attempt  to  base  the  classification  on  relationships.  Very  nearly 
related  animals  are  put  into  the  same  species.  They  are  related 
because  they  descend  from  a  common  ancestry,  and  that  common 
ancestry  could  not  in  most  cases  have  been  very  ancient,  otherwise 
evolution  within  the  group  would  have  occurred  and  the  species  would 
have  been  split  into  two  or  more  species.  Species  that  are  much 
alike  are  included  in  one  genus,  being  thus  marked  off  from  the  species 
of  another  genus.  The  similarity  of  the  species  of  a  genus  is  held  to 
indicate  kinship,  but  since  there  is  greater  diversity  among  the  indi- 
viduals of  a  genus  than  among  the  members  of  a  species,  the  common 
stock  from  which  the  species  of  a  genus  have  sprung  must  have  existed 
at  an  earlier  time,  in  order  that  evolution  could  bring  about  the  degree 
of  divergence  now  observed.  In  like  manner,  a  family  is  made  up  of 
genera,  and  their  likeness  is  again  a  sign  of  affinity.  But  to  account 
for  the  greater  difference  between  the  extreme  individuals  belonging  to 
a  family,  evolution  must  have  had  more  time,  that  is,  the  common 
source  of  the  members  of  a  family  must  have  antedated  the  common 
source  of  the  individuals  of  a  genus.  Orders,  classes,  and  phyla  are 
similarly  regarded  as  having  sprung  from  successively  more  remote 
ancestors,  the  time  differences  being  necessary  to  allow  for  the  differ- 
ences in  the  amount  of  evolution.  This  statement  is  in  general  correct. 
However,  since  evolution  has  probably  not  proceeded  at  the  same  rate 
at  all  periods,  nor  in  all  branches  of  the  animal  kingdom  at  any  one 
time,  the  time  relations  of  the  groups  of  high  or  low  rank  must  not  be 
too  rigidly  assigned.  Thus  certain  genera,  in  which  evolution  has  been 
slow,  are  probably  much  older  than  some  families  in  which  evolution 
has  been  rapid.  It  is  not  improbable,  also,  that  some  genera  are  quite 
as  old  as  the  families  which  include  them;  but  in  no  case  can  they  be 
older.  Furthermore,  different  groups  are  classified  by  taxonomists  of 
different  temperaments,  so  that  groups  of  a  given  nominal  rank  may 
be  much  more  inclusive  (and  hence  older)  in  one  branch  of  the  animal 
kingdom  than  in  another.  On  the  whole,  nevertheless,  the  groups  of 
higher  rank  have  sprung  from  ancestry  more  remote  than  that  of  the 
groups  of  lower  rank. 

The  means  of  recognizing  the  kinship  implied  in  classification 
permit  some  differences  of  opinion.     It  is  recognized  that  likeness  in 


EVIDENCES  FROM  CLASSIFICATION  119 

structural  characters  is  the  chief  clue  to  affinities.  However,  the 
evidential  value  of  similarity  in  one  or  several  structures  unaccom- 
panied by  the  similarity  of  all  parts  is  to  be  distrusted,  since  animals 
widely  separated  and  dissimilar  in  most  characters  may  have  certain 
other  features  in  common.  Thus,  the  coots,  phalaropes  and  grebes 
among  birds  have  lobate  feet  but,  as  indicated  by  other  features,  they 
are  not  closely  related;  and  there  are  certain  lizards  (Amphisbaenidae) 
which  closely  resemble  certain  snakes  (Typholopidae)  in  being  blind, 
limbless,  and  having  a  short  tail.  The  early  systematists  were  very 
liable  to  bring  together  in  their  classification  analogous  forms,  that  is, 
those  which  are  functionally  similar;  or  animals  which  are  super- 
ficially similar.  In  contrast  with  the  early  practice,  the  aim  of 
taxonomists  at  the  present  time  is  to  group  forms  according  to  homol- 
ogy, which  is  considered  an  indication  of  actual  relationship.  Since 
a  genetic  classification  must  take  into  consideration  the  entire  animal, 
the  search  for  affinities  becomes  an  attempt  to  evaluate  the  results 
of  all  morphological  knowledge,  and  it  is  also  becoming  evident  that 
other  things  besides  structure  may  throw  light  upon  relationships. 
The  fossil  records,  geographical  distribution,  ecology  and  experi- 
mental breeding  may  all  assist  in  establishing  affinities. 

The  method  of  taxonomy. — It  is  evident  that  before  the  relation- 
ships of  animals  can  be  determined  the  forms  must  be  known,  for 
unknown  forms  constitute  breaks  in  the  pedigrees  of  the  groups  to 
which  they  belong.  Moreover,  as  pointed  out  above,  the  structural 
characters,  variation  and  distribution  must  be  known  before  a  form 
can  be  placed  in  the  proper  place  in  a  genetic  system.  For  these 
reasons  an  important  part  of  systematic  work  is  the  description  of 
forms  and  an  analysis  of  their  differences.  After  the  Linnaean 
system  was  adopted  zoologists  attacked  this  virgin  field  and  for  many 
years  "species  making"  predominated.  Even  at  the  present  time 
when  other  aspects  of  zoology  have  come  to  receive  relatively  more 
attention  it  is  an  interesting  fact  that  the  analytical  method  prevails 
in  systematic  studies,  and  taxonomy  suffers  from,  and  in  part  merits, 
the  criticism  that  it  is  a  mere  cataloging  of  forms  and  ignores  the 
higher  goal  of  investigation,  namely,  the  discovery  of  the  course  of 
evolution.  Many  systematists,  however,  recognize  that  the  ultimate 
purpose  of  taxonomic  work  is  to  discover  the  relationships  as  well  as 
the  differences  between  the  described  forms  in  order  that  the  course  of 
evolution  may  be  determined.  In  other  words,  it  is  appreciated  that 
while  analytical  studies  are  necessary  they  are  only  preliminary,  and 


i20      READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

that  upon  their  results  must  be  built  synthetic  studies,  if  taxonomy 
is  to  fulfil  its  purpose. 

THE   METHOD   OF   CLASSIFICATION 
CHARLES   DARWIN^ 

Naturalists,  as  we  have  seen,  try  to  arrange  the  species,  genera, 
and  families  in  each  class,  on  what  is  called  the  Natural  System.  But 
what  is  meant  by  this  system  ?  Some  authors  look  at  it  merely  as  a 
scheme  for  arranging  together  those  living  objects  which  are  most 
alike,  and  for  separating  those  which  are  most  unlike;  or  as  an  artificial 
method  of  enunciating,  as  briefly  as  possible,  general  propositions, — 
that  is,  by  one  sentence  to  give  the  characters  common,  for  instance, 
to  all  mammals,  by  another  those  common  to  all  carnivora,  by  another 
those  common  to  the  dog-genus,  and  then,  by  adding  a  single  sentence, 
a  full  description  is  given  of  each  kind  of  dog.  The  ingenuity 
and  utiUty  of  this  system  are  indisputable.  But  many  naturalists 
think  that  something  more  is  meant  by  the  Natural  System;  they 
believe  that  it  reveals  the  plan  of  the  Creator;  but  unless  it  be  specified 
whether  order  in  time  or  space,  or  both,  or  what  else  is  meant  by  the 
plan  of  the  Creator,  it  seems  to  me  that  nothing  is  thus  added  to  our 
knowledge.  Expressions  such  as  that  famous  one  by  Linnaeus,  which 
we  often  meet  with  in  a  more  or  less  concealed  form,  namely,  that  the 
characters  do  not  make  the  genus,  but  that  the  genus  gives  the  charac- 
ters, seem  to  imply  that  some  deeper  bond  is  included  in  our  classifica- 
tions than  mere  resemblance.  I  believe  that  this  is  the  case,  and  that 
community  of  descent — the  one  known  cause  of  close  similarity  in 
organic  beings — is  the  bond  which,  though  observed  by  various 
degrees  of  modification,  is  partially  revealed  to  us  by  our  classifications. 

Let  us  now  consider  the  rules  followed  in  classification,  and  the 
difficulties  which  are  encountered  on  the  view  that  classification  either 
gives  some  unknown  plan  of  creation,  or  is  simply  a  scheme  for 
enunciating  general  propositions  and  of  placing  together  the  forms 
most  like  each  other.  It  might  have  been  thought  (and  was  in  ancient 
times  thought)  that  those  parts  of  the  structure  which  determined  the 
habits  of  life,  and  the  general  place  of  each  being  in  the  economy  of 
nature,  would  be  of  very  high  importance  in  classification.  Nothing 
can  be  more  false.  No  one  regards  the  external  similarity  of  a  mouse 
to  a  shrew,  of  a  dugong  to  a  whale,  of  a  whale  to  a  fish,  as  of  any 

^  From  The  Origin  oj  Species. 


EVIDENCES  FROM  CLASSIFICATION  121 

importance.  These  resemblances,  though  so  intimately  connected 
with  the  whole  life  of  the  being,  are  ranked  as  merely  "adaptive  or 
analogical  characters  " :  but  to  the  consideration  of  these  resemblances 
we  shall  recur.  It  may  even  be  given,  as  a  general  rule,  that  the  less 
any  part  of  the  organisation  is  concerned  with  special  habits,  the  more 
important  it  becomes  for  classification.  As  an  instance:  Owen,  in 
speaking  of  the  dugong,  says,  "The  generative  organs,  being  those 
which  are  most  remotely  related  to  the  habits  and  food  of  an  animal, 
I  have  always  regarded  as  affording  very  clear  indications  of  its  true 
affinities.  We  are  least  likely  in  the  modifications  of  these  organs  to 
mistake  a  merely  adaptive  for  an  essential  character."  With  plants 
how  remarkable  it  is  that  the  organs  of  vegetation,  on  which  their 
nutrition  and  life  depend,  are  of  little  signification;  whereas  the 
organs  of  reproduction,  with  their  product  the  seed  and  embryo,  are 
of  paramount  importance!  So  again  in  formerly  discussing  certain 
morphological  characters  which  are  not  functionally  important,  we 
have  seen  that  they  are  often  of  the  highest  service  in  classification. 
This  depends  on  their  constancy  throughout  many  allied  groups;  and 
their  constancy  chiefly  depends  on  any  slight  deviations  not  having 
been  preserved  and  accumulated  by  natural  selection,  which  acts  only 
on  serviceable  characters. 

WHAT  IS  A  SPECIES? 

"Each  kind  of  animal  or  plant,  that  is,  each  set  of  forms  which 
in  the  changes  of  the  ages  has  diverged  tangibly  from  its  neighbors, 
is  called  a  species.  There  is  no  absolute  definition  for  the  word 
species.  The  word  kind  represents  it  exactly  in  common  language, 
and  is  just  as  susceptible  to  exact  definition.  The  scientific  idea  of 
species  does  not  differ  materially  from  the  popular  notion.  A  kind  of 
tree  or  bird  or  squirrel  is  a  species.  Those  individuals  which  agree 
very  closely  in  structure  and  function  belong  to  the  same  species. 
There  is  no  absolute  test,  other  than  the  common  judgment  of  men 
competent  to  decide.  Naturalists  recognize  certain  formal  rules  as 
assisting  in  such  a  decision.  A  series  of  fully  intergrading  forms, 
however  varied  at  the  extremes,  is  usually  regarded  as  forming  a  single 
species.  There  are  certain  recognized  effects  of  chmate,  of  climatic 
isolation,  and  of  the  isolation  of  domestication.  These  do  not  usually 
make  it  necessary  to  regard  as  distinct  species  the  extreme  forms  of 
a  series  concerned."^ 

^  From  D.  S.  Jordan  and  V.  L.  Kellogg,  Evolution  and  Animal  Li/e. 


122     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

"The  term  'species'  was  thus  defined  by  the  celebrated  botanist 
De  Candolle:  'A  species  is  a  collection  of  all  the  individuals  which 
resemble  each  other  more  than  they  resemble  anything  else,  which  can 
by  mutual  fecundation  produce  fertile  individuals,  and  which  repro- 
duce themselves  by  generation,  in  such  a  manner  that  we  may  from 
analogy  suppose  them  all  to  have  sprung  from  one  single  individual.' 
And  the  zoologist  Swainson  gives  a  somewhat  similar  definition :  'A 
species,  in  the  usual  acceptation  of  the  term,  is  an  animal  which,  in 
a  state  of  nature,  is  distinguished  by  certain  peculiarities  of  form,  size, 
colour,  or  other  circumstances,  from  another  animal.  It  propagates, 
after  its  kind,  individuals  perfectly  resembling  the  parent;  its  pecu- 
liarities, therefore,  are  permanent.'  "  ^ 

[As  will  have  become  apparent,  the  fundamental  assumption 
underlying  classification  is  that  the  closest  fundamental  similarities 
between  animals  (or  plants)  are  found  in  the  forms  most  closely 
related  and  that  the  greatest  differences  are  found  in  those  forms  which 
are  unrelated  or  at  best  very  distantly  related.  The  assumption 
implies  the  idea  of  descent  with  modification,  which  is  no  more  nor 
less  than  evolution.  Using  this  evolutionary  basis,  we  can  arrive  at 
an  extremely  satisfactory  classification  both  of  living  and  of  extinct 
forms;  and  there  is  no  other  basis  of  classification  that  works. 

The  question  might  well  be  asked  whether  it  is  possible  to  test  the 
validity  of  the  assumption  that  degrees  of  resemblance  vary  directly 
with  closeness  of  blood  relationship  ?  Two  direct  tests  of  this  may 
be  and  have  been  made.  The  closest  of  blood  relatives  possible  are 
individuals  that  have  been  derived  by  the  dividing  of  a  single  egg. 
Armadillo^  quadruplets  have  been  shown  to  be  thus  derived,  and 
detailed  studies  of  the  closeness  of  resemblance  existing  between 
members  of  a  given  set  indicate  that  they  are  vastly  more  alike  than 
are  the  simultaneously  born  offspring  of  animals  which  give  birth  to 
several  young,  but  in  which  each  young  is  derived  from  a  separate  egg. 
If  we  use  the  index  of  correlation  to  indicate  the  degree  of  similarity 
between  individuals  we  find  that  ordinary  brothers  or  sisters  are  only 
about  50  per  cent  alike,  while  armadillo  quadruplets  are  over  90  per 
cent  alike.  Identical  or  duplicate  twins  in  human  beings  are  believed 
to  have  an  origin  from  one  egg,  after  the  fashion  of  the  armadillo, 

^  From  A.  R.  Wallace,  Daricinism. 

2  See  H.  H.  Newman,  The  Biology  of  Twins  (191 7),  University  of  Chicago 
Press. 


EVIDENCES  FROM  CLASSIFICATION 


123 


though  the  proof  has  not  been  forthcoming.  Everyone  is  famihar 
with  the  remarkable  similarity,  amounting  almost  to  identity,  between 
such  twins.  Thus  we  are  able  to  show  that  the  closest  blood  relation- 
ship known  is  associated  with  the  closest  resemblance.  The  next 
degree  of  resemblance  is  between  members  of  the  same  family, 
brothers,  sisters,  cousins,  etc.,  and  we  do  not  hesitate  to  explain  this 
resemblance  as  due  to  blood  relationship.  In  this  we  merely  accept 
the  known  principles  of  heredity. 

The  second  direct  test  of  the  validity  of  the  assumption  that 
degrees  of  resemblance  run  parallel  with  degrees  of  blood  relationship 
is  found  in  connection  with  ''  blood- transfusion  tests."  This  evidence, 
as  presented  by  Professor  Scott,  forms  the  substance  of  the  next 
chapter. — Ed.] 


CHAPTER  IX 
EVIDENCE  FROM  BLOOD  TESTS^ 

« 

W.  B.  Scott 

Here  may  be  conveniently  considered  the  very  interesting  and 
significant  blood  tests  which  have  been  made  in  the  last  fifteen  years 
by  various  physiologists  and  especially  by  Dr.  George  H.  F.  Nuttall, 
of  the  University  of  Cambridge.  Though  there  are  several  methods 
of  making  these  tests,  the  "precipitation  method"  employed  by 
Dr.  Nuttall  will  be  quite  sufficient  for  the  ends  sought  in  these  lec- 
tures. The  method  and  significance  of  the  tests  can  best  be  explained 
bv  taking  as  an  example  human  blood,  which,  of  course,  has  been  most 
extensively  and  minutely  studied,  because  of  its  legal  importance  as 
well  as  its  scientific  interest.  Ordinary  chemical  analysis  is  unable 
to  determine  the  differences  in  blood-composition  between  various 
animals,  but  that  there  were  important  differences  had  long  been 
understood.  This  was  shown  by  the  fact  that,  in  performing  the 
operation  for  the  transfusion  of  blood,  it  was  not  practicable  to 
substitute  animal  for  human  blood,  since  the  former  might  cause 
serious  injury  to  the  patient.  ' 

The  precipitation  method  of  making  blood  tests  is  as  follows: 
Freshly  drawn  human  blood  is  allowed  to  coagulate  or  clot,  which  it 
will  do  in  a  few  minutes,  if  left  standing  in  a  dish,  and  then  the  serum 
is  drained  away  from  the  clot.  Blood-serum  is  the  watery,  almost 
colourless  part  of  the  blood,  which  remains  after  coagulation.  Small 
quantities  of  this  serum  are  injected,  at  intervals  of  one  or  two  days, 
into  the  veins  of  a  rabbit  and  cause  the  formation  in  the  rabbit's  blood 
of  an  anti-body,  analogous  to  the  anti-toxin  which  is  produced  in  the 
blood  of  a  horse  by  the  injection  of  diphtheria  virus.  After  the  last 
injection  the  rabbit  is  allowed  to  live  for  several  days  and  is  then 
killed  and  bled,  the  blood  is  left  until  it  clots  and  the  serum  drained 
off  and  preserved.  The  serum  obtained  thus  from  a  rabbit  is  called 
''anti-human"  serum  and  is  an  exceedingly  deUcate  test  for  human 
blood,  not  only  when  the  latter  is  fresh,  but  also  when  it  is  in 
the  form  of  old  and  dried  blood-stains,  or  even  when  the  blood  is 

^  From  W.  B.  Scott,  The  Theory  of  Evolution  (copyright  1917)-  Used  by 
special  permission  of  the  publishers,  The  Macmillan  Company. 

124 


EVIDENCE  FROM  BLOOD  TESTS  125 

putrid.  Stains,  for  example,  are  soaked  in  a  very  weak  solution  of 
common  salt  and,  if  necessary,  the  blood  solution  is  filtered  until  it  is 
quite  limpid  and  clear.  Into  the  blood  solution  a  few  drops  of  the 
anti-human  serum  are  conveyed  and,  if  the  stains  are  of  human  blood, 
a  white  precipitate  is  formed  and  thrown  down,  but  if  the  stains  are 
of  the  blood  of  some  domestic  animal,  such  as  a  pig,  sheep,  or  fowl, 
no  such  reaction  follows.  In  the  same  manner  as  above  described, 
we  may  prepare  anti-pig,  anti-horse,  anti-fowl,  etc.,  etc.,  sera  by 
injecting  the  fresh-drawn  serum  of  a  pig,  horse,  fowl,  or  any  other 
animal  into  the  rabbit,  instead  of  human  blood-serum.  In  some 
countries,  notably  in  Germany  and  Austria,  this  test  has  already  been 
adopted  by  the  courts  of  justice  and  has  been  found  extremely  useful 
in  the  detection  of  crime. 

Further  investigation  showed  that  these  blood  tests  might  be 
employed  to  determine  the  degrees  of  relationship  between  different 
animals,  for,  although  a  prompt  and  strong  reaction  is  usually  obtained 
only  from  the  blood  of  the  same  species  as  that  from  which  the  original 
injection  into  the  rabbit  was  taken,  the  blood  of  nearly  allied  species, 
such  as  the  horse  and  donkey,  for  example,  gives  a  weaker  and  slower 
precipitation.  By  using  stronger  solutions  and  allowing  more  time, 
quite  distant  relationships  may  be  brought  out.  Nuttall  and  his 
collaborator,  Graham-Smith,  made  many  thousands  of  such  experi- 
ments bearing  upon  the  problems  of  relationship  and  classification 
and  it  is  of  great  significance  to  note  that  their  highly  interesting 
and  important  results  contain  few  surprises,  but,  in  almost  all  cases, 
merely  serve  to  confirm  the  conclusions  previously  reached  by  other 
methods,  such  as  comparative  anatomy  and  palaeontology.  It  will 
be  instructive  to  quote  some  of  these  results,  the  quotations  being 
taken  from  "Blood  Immunity  and  Blood  Relationship,  by  G.  H.  F. 
Nuttall,  including  Original  Researches  by  G.  L.  Graham-Smith  and 
T.  S.  P.  Strangeways, "  Cambridge,  1904. 

''In  the  absence  of  palaeontological  evidence  the  question  of  the 
interrelationship  amongst  animals  is  based  upon  similarities  of  struc- 
ture in  existing  forms.  In  judging  of  these  similarities,  the  subjective 
element  may  largely  enter."  ''The  very  interesting  observations 
upon  the  eye  made  by  Johnson  also  demonstrate  the  close  relationships 
between  the  Old  World  forms  and  man,  the  macula  lutea  tending  to 
disappear  as  we  descend  in  the  scale  of  New  World  Monkeys  and  being 
absent  in  the  Lemurs.  The  results  which  I  published  upon  my  tests 
with  precipitins  directly  supported  this  evidence,  for  the  reactions 


126     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

obtained  with  the  bloods  of  Simiidae  (i.e.,  Man-Hke  Apes)  closely 
resemble  those  obtained  with  human  blood,  the  bloods  of  Cercopithe- 
cidae  (Old  World  Monkeys)  came  next,  followed  by  those  of  Cebidae 
and  Hapalidae  (New  World  Monkeys  and  Marmosets)  which  gave 
but  slight  reactions  with  anti-human  serum,  whilst  the  blood  of 
Lemuroidea  gave  no  indication  of  blood-relationship."  "A  perusal 
of  the  pages  relating  to  the  tests  made  upon  the  many  bloods  I  have 
examined  by  means  of  precipitating  anti-sera,  will  very  clearly  show 
that  this  method  of  investigation  permits  of  our  drawing  certain 
definite  conclusions.  It  is  a  remarkable  fact  ....  that  a  common 
property  has  persisted  in  the  bloods  of  certain  groups  of  animals 
throughout  the  ages  which  have  elapsed  during  their  evolution  from 
a  common  ancestor,  and  this  in  spite  of  differences  of  food  and  habits 
of  life.  The  persistence  of  the  chemical  blood-relationship  between 
the  various  groups  of  animals  serves  to  carry  us  back  into  geological 
times,  and  I  beheve  we  have  but  begun  the  work  along  these  lines, 
and  that  it  will  lead  to  valuable  results  in  the  study  of  various  problems 
of  evolution." 

The  general  conclusions  on  interrelationships,  so  far  as  they  are  of 
particular  interest  for  our  purpose,  reached  by  Nuttall  and  Graham- 
Smith  as  the  result  of  many  thousands  of  blood  tests,  may  be  summa- 
rized as  follows: 

I.  If  sufficiently  strong  solutions  be  used  and  time  enough  be 
allowed,  a  relationship  between  the  bloods  of  all  mammals  is  made 
evident. 

.   2.  The  degrees  of  relationship  between  man,  apes  and  monkeys 
have  already  been  noted. 

3.  Anti-carnivore  sera  show  ''a  preponderance  of  large  reactions 
amongst  the  bloods  of  Carnivora,  as  distinguished  from  other  Mam- 
malia; the  maximum  reactions  usually  take  place  amongst  the  more 
closely  related  forms  in  the  sense  of  descriptive  zoology." 

4.  Anti-pig  serum  gives  maximum  reactions  only  with  the  bloods 
of  other  species  of  the  same  family,  moderate  reactions  those  of  rumi- 
nants and  camels,  and  moderate  or  slight  reactions  with  those  of 
whales.  Anti-llama  serum  gives  a  moderate  reaction  with  the  blood  of 
the  camel,  and  the  close  relationship  between  the  deer  family  and  the 
great  host  of  antelopes,  sheep,  goats  and  oxen  is  clearly  demonstrated. 

5.  An ti- whale  serum  gives  maximum  reactions  only  with  the 
bloods  of  other  whales  and  slight  reactions  with  those  of  pigs  and 
ruminants. 


EVIDENCE  FROM  BLOOD  TESTS  127 

6.  A  close  relationship  is  shown  to  exist  between  all  marsupials, 
with  the  exception  of  the  Thylacine,  or  so-called  Tasmanian  Wolf. 

7.  Strong  anti-turtle  serum  gives  maximum  reactions  only  with 
the  bloods  of  turtles  and  crocodiles;  with  those  of  lizards  and  snakes 
the  results  are  almost  negative.  With  the  egg-albumins  of  reptiles 
and  birds  a  moderate  reaction  is  given. 

8.  Anti-lizard  serum  produces  maximum  results  with  the  bloods 
of  lizards  and  reacts  well  with  those  of  snakes. 

9.  These  experiments  indicate  that  there  is  a  close  relationship 
between  lizards  and  snakes,  on  the  one  hand,  turtles  and  crocodiles 
on  the  other.  They  further  indicate  that  birds  are  more  nearly  allied 
with  the  turtle-crocodile  series  than  with  the  lizard-snake  series, 
results  for  which  palaeontological  studies  had  already  prepared  us. 

-  10.  ''Tests  were  made  by  means  of  anti-sera  for  the  fowl  and 
ostrich  upon  792  and  649  bloods  respectively.  They  demonstrate  a 
similarity  in  blood  constitution  of  all  birds,  which  was  in  sharp  con- 
trast to  what  had  been  observed  with  mammalian  bloods,  when  acted 
upon  by  anti-mammahan  sera.  Differences  in  the  degree  of  reaction 
were  observed,  but  did  not  permit  of  drawing  any  conclusions." 

II.  I  have  already  called  attention  to  the  fact  that  the  prob- 
lematical Horseshoe-crab  is  indicated  by  its  embryology  to  be  related 
to  the  air-breathing  spiders  and  scorpions  rather  than  to  the  marine 
Crustacea.  It  is  of  exceptional  interest  to  learn  that  embryology  is 
supported  by  the  results  of  the  blood  tests. 

It  must  not  be  supposed  that  there  is  any  exact  mathematical 
ratio  between  the  degrees  of  relationship  indicated  by  the  blood  tests 
and  those  which  are  shown  by  anatomical  and  palaeontological 
evidence.  Any  supposition  of  the  kind  would  be  immediately  nega- 
tived by  the  contrast  between  the  blood  of  mammals  and  that  of  birds. 
It  could  hardly  be  maintained  that  an  ostrich  and  a  parrot  are 
more  nearly  allied  than  a  wolf  and  a  hyena  and  yet  that  would  be 
the  inference  from  the  blood  tests.  Like  all  other  anatomical  and 
physiological  characters,  the  chemical  composition  of  the  blood  is 
subject  to  change  in  the  course  of  evolution  and  these  developmental 
changes  do  not  keep  equal  pace  in  all  parts  of  the  organism.  It  is  the 
rule  rather  than  the  exception  to  find  that  one  part  of  the  structure 
advances  much  more  rapidly  than  other  parts,  such  as  the  teeth,  the 
skull,  or  the  feet.  The  human  body  is,  fortunately  for  us,  of  rather 
a  primitive  kind,  while  the  development  of  the  brain  is  far  superior 
to  that  of  any  other  mammal  and  this  great  brain  development  has 


128      READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

necessitated  a  remodeling  of  the  skull.  On  the  other  hand,  the 
skeleton,  limbs,  hands  and  feet  are  but  slightly  specialized.  In  the 
elephant  tribe,  so  far  as  we  can  trace  them  back  in  time,  there  has 
been  little  change,  save  in  size,  in  the  structure  of  the  body  or  limbs , 
while  the  teeth  and  skull  have  passed  through  a  series  of  remarkable 
changes.  It  is  for  this  reason  that  it  is  unsafe  to  found  a  scheme  of 
classification,  which  is  meant  to  be  a  brief  expression  of  relationship, 
upon  a  single  character,  for  the  result  is  almost  invariably  misleading. 
The  results  of  blood  tests  must  be  critically  examined  and  checked  by 
a  comparison  with  the  results  obtained  by  other  methods  of  investiga- 
tion, but  after  every  allowance  has  been  made,  these  tests  are  very 
remarkable. 

The  blood  tests  have  brought  very  strong  confirmation  to  the 
theory  of  evolution  and  from  an  entirely  unexpected  quarter;  they 
come  as  near  to  giving  a  definite  demonstration  of  the  theory  as  we 
are  likely  to  find,  until  experimental  zoology  and  botany  shall  have 
been  improved  and  perfected  far  beyond  their  present  state. 


CHAPTER  X 

EVIDENCES  FROM  MORPHOLOGY 
(COMPARATIVE  ANATOMY)^ 

GEORGE   JOHN    ROMANES 

The  theory  of  evolution  supposes  that  hereditary  characters 
admit  of  being  slowly  modified  wherever  their  modification  will  render 
an  organism  better  suited  to  a  change  in  its  conditions  of  life.  Let 
us,  then,  observe  the  evidence  which  we  have  of  such  adaptive  modifi- 
cations of  structure,  in  cases  where  the  need  of  such  modification  is 
apparent.  We  may  begin  by  again  taking  the  case  of  the  whales  and 
porpoises.  The  theory  of  evolution  infers,  from  the  whole  structure 
of  these  animals,  that  their  progenitors  must  have  been  terrestrial 
quadrupeds  of  some  kind,  which  gradually  became  more  and  more 
aquatic  in  their  habits.  Now  the  change  in  the  conditions  of  their 
life  thus  brought  about  would  have  rendered  desirable  great  modifica- 
tions of  structure.  These  changes  would  have  begun  by  affecting  the 
least  typical — that  is,  the  least  strongly  inherited — structures,  such 
as  the  skin,  claws,  and  teeth.  But,  as  time  went  on,  the  adaptations 
would  have  extended  to  more  typical  structures,  until  the  shape  of 
the  body  would  have  become  affected  by  the  bones  and  muscles 
required  for  terrestrial  locomotion  becoming  better  adapted  for 
aquatic  locomotion,  and  the  whole  outhne  of  the  animal  more  fish-Hke 
in  shape.  This  is  the  stage  which  we  actually  observe  in  the  seals, 
where  the  hind  legs,  although  retaining  all  their  typical  bones,  have 
become  shortened  up  almost  to  rudiments,  and  directed  backwards, 
so  as  to  be  of  no  use  for  walking,  while  serving  to  complete  the  fish-like 
taper  of  the  body  (Fig.  ii).  But  in  the  whales  the  modification  has 
gone  further  than  this  so  that  the  hind  legs  have  ceased  to  be  apparent 
externally,  and  are  only  represented  internally — and  even  this  only 
in  some  species — by  remnants  so  rudimentary  that  it  is  difficult  to 
make  out  with  certainty  the  homologies  of  the  bones;  moreover,  the 
head  and  the  whole  body  have  become  completely  fish-Hke  in  shape 
(Fig.  12).     But  profound  as  are  these  alterations,  they  affect  only 

^  From  G.  J.  Romanes,  Darwin  and  after  Darwin  (copyright  1892).     Used  by 
special  permission  of  the  publishers,  The  Open  Court  Publishing  Company. 

129 


130      READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 


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EVIDENCES  FROM  MORPHOLOGY  131 

those  parts  of  the  organism  which  it  was  for  the  benefit  of  the  organism 
to  have  altered,  so  that  it  might  be  adapted  to  an  aquatic  mode  of 
existence.  Thus  the  arm,  which  is  used  as  a  fin,  still  retains  the  bones 
of  the  shoulder,  fore-arm,  wrist,  and  fingers,  although  they  are  all 
enclosed  in  a  fin-shaped  sack,  so  as  to  render  them  useless  for 
any  purpose  other  than  swimming  (Fig.  13).  Similarly,  the  head, 
although  it  so  closely  resembles  the  head  of  a  fish  in  shape,  still  retains 
the  bones  of  the  mammalian  skull  in  their  proper  anatomical  relations 
to  one  another;  but  modified  in  form  so  as  to  offer  the  least  possible 
resistance  to  the  water.  In  short,  it  may  be  said  that  all  the  modifi- 
cations have  been  effected  with  the  least  possible  divergence  from  the 
typical  mammalian  type,  which  is  compatible  with  securing  so  perfect 
an  adaptation  to  a  purely  aquatic  mode  of  life. 
.  Now  I  have  chosen  the  case  of  the  whale  and  porpoise  group, 
because  they  offer  so  extreme  an  example  of  profound  modification  of 
structure  in  adaptation  to  changed  conditions  of  life.  But  the  same 
thing  may  be  seen  in  hundreds  and  hundreds  of  other  cases.  For 
instance,  to  confine  our  attention  to  the  arm,  not  only  is  the  limb 
modified  in  the  whale  for  swimming,  but  in  another  mammal — the 
bat — it  is  modified  for  flying,  by  having  the  fingers  enormously 
elongated  and  overspread  with  a  membranous  web. 

In  birds,  again,  the  arm  is  modified  for  flight  in  a  wholly  different 
way — the  fingers  here  being  very  short  and  all  run  together,  while  the 
chief  expanse  of  the  wing  is  composed  of  the  shoulder  and  forearm. 
In  frogs  and  lizards,  again,  we  find  hands  more  like  our  own;  but  in 
an  extinct  species  of  flying  reptile  the  modification  was  extreme,  the 
wing  having  been  formed  by  a  prodigious  elongation  of  the  fifth  finger, 
and  a  membrane  spread  over  it  and  the  rest  of  the  hand  (Fig.  14). 
Lastly,  in  serpents  the  hand  and  arm  have  disappeared  altogether. 

Thus,  even  if  we  confine  our  attention-  to  a  single  organ,  how 
wonderful  are  the  modifications  which  it  is  seen  to  undergo,  although 
never  losing  its  typical  character.  Everywhere  we  find  the  distinction 
between  homology  and  analogy  which  was  explained  in  the  last 
chapter — the  distinction,  that  is,  between  correspondence  of  structure 
and  correspondence  of  function.  On  the  one  hand,  we  meet  with 
structures  which  are  perfectly  homologous  and  yet  in  no  way 
analogous;  the  structural  elements  remain,  but  are  profoundly 
modified  so  as  to  perform  wholly  different  functions.  On  the  other 
hand,  we  meet  with  structures  which  are  perfectly  analogous,  and 
yet  in  no  way  homologous;  totally  different  structures  are  modified 


1^2      READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 


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EVIDENCES  FROM  MORPHOLOGY 


133 


to  perform  the  same  functions.  How,  then,  are  we  to  explain  these 
things  ?  By  design  manifested  in  special  creation,  or  by  descent  with 
adaptive  modification  ?  If  it  is  said  by  design  manifested  in  special 
creation,  we  must  suppose  that  the  Deity  formed  an  archetypal 
plan  of  certain  structures,  and  that  he  determined  to  adhere  to  this 
plan  through  all  the  modifications  which  those  structures  exhibit.  But, 
if  so,  why  is  it  that  some  structures  are  selected  as  typical  and  not 
others  ?     Why  should  the  vertebral  skeleton,  for  instance,  be  tortured 


Fig.  13. — Paddle  of  whale  compared  with  hand  of  man.     {From  Romanies.) 


into  every  conceivable  variety  of  modification  in  order  to  subserve  as 
great  a  variety  of  functions;  while  another  structure,  such  as  the  eye, 
is  made  in  different  sub-kingdoms  on  fundamentally  different  plans, 
notwithstanding  that  it  has  throughout  to  perform  the  same  func- 
tion ?  Will  any  one  have  the  hardihood  to  assert  that  in  the  case  of 
the  skeleton  the  Deity  has  endeavored  to  show  his  ingenuity,  by  the 
manifold  functions  to  which  he  has  made  the  same  structure  sub- 
servient; while  in  the  case  of  the  eye  he  has  endeavored  to  show  his 
resources,  by  the  manifold  structures  which  he  has  adapted  to  serve 
the  same  function?  If  so,  it  becomes  a  most  unfortunate  circum- 
stance that,  throughout  bo.th  the  vegetable  and  animal  kingdoms,  all 
cases  which  can  be  pointed  to  as  showing  ingenious  adaptation  of  the 


134     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 


Fig.  14. — Wing  of  reptile,  mammal,  and  bird.     [From  Romanes?) 


EVIDENCES  FROM  MORPHOLOGY  135 

same  typical  structure  to  the  performance  of  widely  different  func- 
tions— or  cases  of  homology  without  analogy — are  cases  which  come 
within  the  limits  of  the  same  natural  group  of  plants  and  animals,  and 
therefore  admit  of  being  equally  well  explained  by  descent  from  a 
common  ancestry;  while  all  cases  of  widely  different  structures  per- 
forming the  same  function — or  cases  of  analogy  without  homology, 
are  to  be  found  in  different  groups  of  plants  or  animals,  and  are 
therefore  suggestive  of  independent  variations  arising  in  the  different 
lines  of  hereditary  descent. 

To  take  a  specific  illustration.  The  octopus,  or  devil-fish,  belongs 
to  a  widely  different  class  of  animals  from  a  true  fish;  and  yet  its  eye, 
in  general  appearance,  looks  wonderfully  like  the  eye  of  a  true  fish. 
Now,  Mr.  Mivart  pointed  to  this  fact  as  a  great  difficulty  in  the  way 
of  the  theory  of  evolution  by  natural  selection,  because  it  must  clearly 
be  a  most  improbable  thing  that  so  complicated  a  structure  as  the  eye 
of  a  fish  should  happen  to  be  arrived  at  through  each  of  two  totally 
different  lines  of  descent.  And  this  difficulty  would,  indeed,  be  a 
formidable  one  to  the  theory  of  evolution,  if  the  similarity  were  not 
only  analogical  but  homological.  Unfortunately  for  the  objection, 
however,  Darwin  clearly  showed  in  his  reply  that  in  no  one  anatomical 
or  homologous  feature  do  the  two  structures  resemble  one  another; 
so  that,  in  point  of  fact,  the  two  organs  do  not  resemble  one  another 
in  any  particular  further  than  it  is  necessary  that  they  should,  if  both 
are  to  be  analogous,  or  to  serve  the  same  function  as  organs  of  sight. 
But  now,  suppose  that  this  had  not  been  the  case,  and  that  the  two 
structures,  besides  presenting  the  necessary  superficial  or  analogical 
resemblance,  had  also  presented  an  anatomical  or  homologous  resem- 
blance, with  what  force  might  it  have  then  been  urged, — your  hypo- 
thesis of  hereditary  descent  with  progressive  modification  being  here 
excluded  by  the  fact  that  the  animals  compared  belong  to  two  widely 
different  branches  of  the  tree  of  life,  how  are  we  to  explain  the  identity 
of  type  manifested  by  these  two  complicated  organs  of  vision  ?  The 
only  hypothesis  open  to  us  is  intelligent  adherence  to  an  ideal  plan  or 
mechanism.  But  as  this  cannot  now  be  urged  in  any  comparable 
case  throughout  the  whole  organic  world,  we  may,  on  the  other  hand, 
present  it  as  a  most  significant  fact,  that  while  within  the  limits  of  the 
same  large  branch  of  the  tree  of  life  we  constantly  find  the  same 
typical  structures  modified  so  as  to  perform  very  different  functions, 
we  never  find  any  of  these  particular  types  of  structure  in  other  large 
branches  of  the  tree.     That  is  to  say,  we  never  find  typical  structures 


136      READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

appearing  except  in  cases  where  their  presence  may  be  explained  by 
the  hypothesis  of  hereditary  descent;  while  in  thousands  of  such  cases 
we  find  these  structures  undergoing  every  conceivable  variety  of 
adaptive  modification. 

Consequently,  special  creationists  must  fall  back  upon  another 
position  and  say, — Well,  but  it  may  have  pleased  the  Deity  to  form 
a  certain  number  of  ideal  types,  and  never  to  have  allowed  the 
structures  occurring  in  one  type  to  appear  in  any  of  the  others.  We 
answer, — Undoubtedly  such  may  have  been  the  case;  but,  if  so,  it  is 
a  most  unfortunate  thing  for  your  theory,  because  the  fact  implies 
that  the  Deity  has  planned  his  types  in  such  a  way  as  to  suggest  the 
counter-theory  of  descent.  For  instance,  it  would  seem  most  capri- 
cious on  the  part  of  the  Deity  to  have  made  the  eyes  of  an  innumerable 
number  of  fish  on  exactly  the  same  ideal  type,  and  then  to  have  made 
the  eye  of  the  octopus  so  exactly  like  these  other  eyes  in  superficial 
appearance  as  to  deceive  so  accomplished  a  naturalist  as  Mr.  Mivart, 
and  yet  to  have  taken  scrupulous  care  that  in  no  one  ideal  particular, 
should  the  one  type  resemble  the  other.  However,  adopting  for  the 
sake  of  argument  this  great  assumption,  let  us  suppose  that  God  did 
lay  down  these  arbitrary  rules  for  his  own  guidance  in  creation,  and 
then  let  us  see  to  what  the  assumption  leads.  If  the  Deity  formed  a 
certain  number  of  ideal  t3^es,  and  determined  that  on  no  account 
should  he  allow  any  part  of  one  type  to  appear  in  any  part  of  another, 
surely  we  should  expect  that  within  the  limits  of  the  same  type  the 
same  typical  structures  should  always  be  present.  Thus,  remember 
what  efforts,  so  to  speak,  have  been  made  to  maintain  the  uniformity 
of  type  in  the  case  of  the  fore-limb  as  previously  explained,  and  should 
we  not  expect  that  in  other  and  similar  cases  a  similar  method  should 
have  been  followed  ?  Yet  we  repeatedly  find  that  this  is  not  the  case. 
Even  in  the  whale,  as  we  have  seen,  the  hind-limbs  are  either  alto- 
gether absent  or  dwindled  almost  to  nothing;  and  it  is  impossible  to  see 
in  what  respects  the  hind-limbs  are  of  any  less  ideal  value  than  the 
fore-Hmbs — which  are  carefully  preserved  in  all  vertebrated  animals 
except  the  snake,  and  the  extinct  Dinornis,  where  again  we  meet  in 
this  particular  with  a  sudden  and  sublime  indifference  to  the  main- 
tenance of  a  typical  structure  (Fig.  15).  Now  I  say  that  if  the  theory 
of  ideal  tj^^es  is  true,  we  have  in  these  facts  evidence  of  a  most  unrea- 
sonable inconsistency.  But  the  theory  of  descent  with  continued 
adaptive  modification  fully  explains  all  the  known  cases;  for  in  every 
case  the  degree  of  divergence  from  the  typical  structure  which  an 


EVIDENCES  FROM  MORPHOLOGY 


137 


organism  presents  corresponds,  in  a  general  way,  with  the  length  of 
time  during  which   the  divergence  has  been  going  on.     Thus  we 


^ihE  VieV  of  Sr£Rj{jfv\  yA  ■ 


7^'^y/' 


Fig.  15. — Skeleton  of  Dinornis  gravis,  y^  nat.  size.  Drawn  from  nature 
(British  Museum).  As  separate  cuts  on  a  larger  scale  are  shown,  (i)  the  sternum 
as  this  appears  in  mounted  specimens,  and  (2)  the  same  in  profile,  with  its 
(hypothetical)  scapulo-coracoid  attached.     {From  Romanes.) 

scarcely  ever  meet  with  any  great  departure  from  the  typical  form 
with  respect  to  one  of  the  organs,  without  some  of  the  other  organs 
being  so  far  modified  as  of  themselves  to  indicate,  on  the  supposition 


138     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENIC  S 

of  descent  with  modification  that  the  animal  or  plant  must  have  been 
subject  to  the  modifying  influences  for  an  enormously  long  series  of 
generations.  And  this  combined  testimony  of  a  number  of  organs  in 
the  same  organism  is  what  the  theory  of  descent  would  lead  us  to 
expect,  while  the  rival  theory  of  design  can  offer  no  explanation  of  the 
fact,  that  when  one  organ  shows  a  conspicuous  departure  from  the 
supposed  ideal  type,  some  of  the  other  organs  in  the  same  organism 
should  tend  to  keep  it  company  by  doing  likewise. 

As  an  illustration  both  of  this  and  of  other  points  which  have  been 
mentioned,  I  may  draw  attention  to  what  seems  to  me  a  particularly 
suggestive  case.  So-called  soldier-  or  hermit-crabs  are  crabs  which 
have  adopted  the  habit  of  appropriating  the  empty  shells  of  moUusks. 
In  association  with  this  peculiar  habit,  the  structure  of  these  animals 
differs  very  greatly  from  that  of  all  other  crabs.  In  particular,  the 
hinder  part  of  the  body,  which  occupies  the  mollusk-shell,  and  which 
therefore  has  ceased  to  require  any  hard  covering  of  its  own,  has  been 
suffered  to  lose  its  calcareous  integument,  and  presents  a  soft  fleshy 
character,  quite  unlike  that  of  the  most  exposed  parts  of  the  animal. 
Moreover,  this  soft  fleshy  part  of  the  creature  is  especially  adapted  to 
the  particular  requirements  of  the  creature  by  having  its  lateral 
appendages — i.e.,  appendages  which  in  other  Crustacea  perform  the 
function  of  legs —  modified  so  as  to  act  as  claspers  to  the  inside  of  the 
mollusk-shell;  while  the  tail-end  of  the  part  in  question  is  twisted 
into  the  form  of  a  spiral,  which  fits  into  the  spiral  of  the  mollusk-shell. 
Now,  in  Keeling  Island  there  is  a  large  kind  of  crab  called  Birgus  latro, 
which  lives  upon  land  and  there  feeds  upon  cocoa-nuts.  The  whole 
structure  of  this  crab,  it  seems  to  me,  unmistakably  resembles  the 
structure  of  a  hermit-crab  (Fig.  16).  Yet  this  crab  neither  lives  in 
the  shell  of  a  mollusk,  nor  is  the  hinder  part  of  its  body  in  the  soft  and 
fleshy  condition  just  described;  on  the  contrary,  it  is  covered  with  a 
hard  integument  like  all  the  other  parts  of  the  animal.  Consequently, 
I  think  we  may  infer  that  the  ancestors  of  Birgus  were  hermit-crabs 
living  in  mollusk-shells;  but  that  their  descendants  gradually  relin- 
quished this  habit  as  they  gradually  became  more  and  more  terrestrial, 
while,  concurrently  with  these  changes  in  habit,  the  originally  soft 
posterior  parts  acquired  a  hard  protective  covering  to  take  the  place 
of  that  which  was  formerly  supplied  by  a  mollusk-shell.  So  that,  if 
so,  we  now  have,  within  the  limits  of  a  single  organism  evidence  of 
a  whole  series  of  morphological  changes  in  the  past  history  of  its 
species.     First,   there  must  have  been   the  great  change  from  an 


EVIDENCES  FROM  MORPHOLOGY 


139 


i^^'^^V, 


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vi-i       CA 


I40      READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

ordinary  crab  to  a  hermit-crab  in  all  the  respects  previously  pointed 
out.  Next,  there  must  have  been  the  change  back  again  from  a 
hermit-crab  to  an  ordinary  crab,  so  far  as  living  without  the  necessity 
of  a  mollusk-shell  is  concerned.  From  an  evolutionary  ppint  of  view, 
therefore,  we  appear  to  have  in  the  existing  structure  of  Birgus  a 
morphological  record  of  all  these  changes,  and  one  which  gives  us  a 
reasonable  explanation  of  why  the  animal  presents  the  extraordinary 
appearance  which  it  does.  But,  on  the  theory  of  special  creation,  it 
is  inexplicable  why  this  land-crab  should  have  been  formed  on  the 
pattern  of  a  hermit-crab,  when  it  never  has  need  to  enter  the  shell  of 
a  mollusk.  In  other  words,  its  peculiar  structure  is  not  especially  in 
keeping  with  its  present  habits,  although  so  curiously  allied  to  the 
similar  structure  of  certain  other  crabs  of  totally  different  habits,  in 
relation  to  which  the  peculiarities  are  of  plain  and  obvious  significance. 

I  will  devote  the  remainder  of  this  chapter  to  considering  another 
branch  of  the  argument  from  morphology,  to  which  the  case  of  Birgus 
serves  as  a  suitable  introduction:  I  mean  the  argument  from  rudi- 
mentary structures. 

Throughout  both  the  animal  and  vegetable  kingdoms  we  con- 
stantly meet  with  dwarfed  and  useless  representatives  of  organs,  which 
in  other  and  alUed  kinds  of  animals  and  plants  are  of  large  size  and 
functional  utility.  Thus,  for  instance,  the  unborn  whale  has  rudi- 
mentary teeth,  which  are  never  destined  to  cut  the  gums;  and 
throughout  its  life  this  animal  retains,  in  a  similarly  rudimentary 
condition,  a  number  of  organs  which  never  could  have  been  of  use  to 
any  kind  of  creature  save  a  terrestrial  quadruped.  The  whole 
anatomy  of  its  internal  ear,  for  example,  has  reference  to  hearing  in 
air,  as  Hunter  long  ago  remarked,  ''is  constructed  upon  the  same 
principle  as  in  the  quadruped";  yet,  as  Owen  says,  "the  outer  open- 
ing and  passage  leading  therefrom  to  the  tympanum  can  rarely  be 
affected  by  sonorous  vibrations  of  the  atmosphere,  and  indeed  they 
are  reduced,  or  have  degenerated,  to  a  degree  which  makes  it  difficult 
to  conceive  how  such  vibrations  can  be  propagated  to  the  ear-drum 
during  the  brief  moments  in  which  the  opening  may  be  raised  above 
the  water." 

Now,  rudimentary  organs  of  this  kind  are  of  such  frequent  occur- 
rence, that  almost  every  species  presents  one  or  more  of  them — • 
usually,  indeed,  a  considerable  number.  How,  then,  are  they  to  be 
accounted  for  ?  Of  course  the  theory  of  descent  with  adaptive  modi- 
fication has  a  simple  answer  to  supply — namely,  that  when,  from 


EVIDENCES  FROM  MORPHOLOGY 


141 


changed  conditions  of  life,  an  organ  which  was  previously  useful 
becomes  useless,  it  will  be  suffered  to  dwindle  away  in  successive 
generations,  under  the  influence  of  certain  natural  causes  which  we 
shall  have  to  consider  in  future  chapters.  On  the  other  hand,  the 
theory  of  special  creation  can  only  maintain  that  these  rudiments  are 
formed  for  the  sake  of  adhering  to  an  ideal  type.  Now,  here  again 
the  former  theory  appears  to  be  triumphant  over  the  latter;  for, 
without  waiting  to  dispute  the  wisdom  of  making  dwarfed  and  useless 
structures  merely  for  the  whimsical  motive  assigned,  surely  if  such  a 


f^ifK 


KJ 


A'>OllA£flrAIKy  h///p-Ll/ylBS 


A .      \lEfjT, 


Fig.  17. — Rudimentary  or  vestigial  hind  limbs  of  python,  as  exhibited  in  the 
skeleton  and  on  the  external  surface  of  the  animal.  Drawn  from  nature,  \  nat. 
size.     {From  Romanes.) 


method  were  adopted  in  so  many  cases,  we  should  expect  that  in  con- 
sistency it  would  be  adopted  in  all  cases.  This  reasonable  expectation, 
however,  is  far  from  being  realized.  We  have  already  seen  that  in 
numberless  cases,  such  as  that  of  the  fore-limbs  of  serpents,  no  vestige 
of  a  rudiment  is  present.  But  the  vacillating  policy  in  the  matter  of 
rudiments  does  not  end  here ;  for  it  is  shown  in  a  still  more  aggravated 
form  where  within  the  limits  of  the  same  natural  groups  of  organisms 
a  rudiment  is  sometimes  present  and  sometimes  absent.  For  instance, 
although  in  nearly  all  the  numerous  species  of  snakes  there  are 
no  vestiges  of  limbs,  in  the  Python  we  find  very  tiny  rudiments  of 
the  hind-limbs  (Fig.  17).  Now,  is  it  a  worthy  conception  of  Deity 
that,  while  neglecting  to  maintain  his  unity  of  ideal  in  the  case  of 


142      READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

nearly  all  the  numerous  species  of  snakes,  he  should  have  added  a  tiny 
rudiment  in  the  case  of  the  Python — and  even  in  that  case  should 
have  maintained  his  ideal  very  inefficiently,  inasmuch  as  only  two 
limbs,  instead  of  four,  are  represented  ?  How  much  more  reasonable 
is  the  naturalistic  interpretation;  for  here  the  very  irregularity  of 
their  appearance  in  different  species,  which  constitutes  rudimentary 
structures  one  of  the  crowning  difficulties  to  the  theory  of  special 
design,  furnishes  the  best  possible  evidence  in  favour  of  hereditary 


Fig.  1 8. — Apteryx  australis.  Drawn  from  life  in  the  Zoological  Gardens, 
I  nat.  size.  The  external  wing  is  drawn  to  a  scale  in  the  upper  part  of  the  cut. 
The  surroundings  are  supplied  from  the  most  recent  descriptions.  {From 
Romanes.) 

descent;  seeing  that  this  irregularity  then  becomes  what  may  be 
termed  the  anticipated  expression  of  progressive  dwindling  due  to 
inutility.  Thus,  for  example,  to  return  to  the  case  of  wings,  we  have 
already  seen  that  in  an  extinct  genus  of  bird,  Dinornis,  these  organs 
were  reduced  to  such  an  extent  as  to  leave  it  still  doubtful  whether  so 
much  as  the  tiny  rudiment  hypothetically  supplied  to  Figure  15  was 
present  in  all  the  species.  And  here  is  another  well-known  case  of 
another  genus  of  still  existing  bird,  which,  as  was  the  case  with 
Dinornis,  occurs  only  in  New  Zealand  (Fig.  18).  Upon  this  island 
there  are  no  four-footed  enemies — either  existing  or  extinct — to  escape 
from   which   the  wings  of  birds  would  be  of  any  service.     Conse- 


EVIDENCES  FROM  MORPHOLOGY 


U3 


quently  we  can  understand  why  on  this  island  we  should  meet  with 
such  a  remarkable  dwindling  away  of  wings. 

Similarly,  the  logger-headed  duck  of  South  America  can  only  flap 
along  the  surface  of  the  water,  having  its  wings  considerably  reduced 
though  less  so  than  the  Apteryx  of  New  Zealand.  But  here  the 
interesting  fact  is  that  the  young  birds  are  able  to  fly  perfectly  well. 
Now,  in  accordance  with  a  general  law  to  be  considered  in  a  future 
chapter,  the  life-history  of  an  individual  organism  is  a  kind  of  con- 
densed recapitulation  of  the  life-history  of  its  species.  Consequently, 
we  can  understand  why  the  little  chickens  of  the  logger-headed  duck 
are  able  to  fly  like  all  other  ducks,  while  their  parents  are  only  able 
to  flap  along  the  surface  of  the  water. 

Facts  analogous  to  this  reduction  of  wings  in  birds  which  have  no 
further  use  for  them,  are  to  be  met  with  also  in  insects  under  similar 
circumstances.  Thus,  there  are  on  the  island  of  Madeira  somewhere 
between  500  and  600  species  of  beetles,  which  are  in  large  part  peculiar 
to  that  island,  though  related  to  other — and  therefore  presumably 
parent — species  on  the  neighboring  continent.  Now,  no  less  than  200 
species — or  nearly  half  the  whole  number — are  so  far  deficient  in 
wings  that  they  cannot  fly.  And,  if  we  disregard  the  species  which 
are  not  peculiar  to  the  island — that  is  to  say,  all  the  species  which 
likewise  occur  on  the  neighboring  continent,  and  therefore,  as  evolu- 
tionists conclude,  have  but  recently  migrated  to  the  island, — we  find 
this  very  remarkable  proportion.  There  are  altogether  29  peculiar 
genera,  and  out  of  these  no  less  than  2t,  have  all  their  species  in  this 
condition. 

Similar  facts  have  been  recently  observed  by  the  Rev.  A.  E.  Eaton 
with  respect  to  insects  inhabiting  Kerguelen  Island.  All  the  species 
which  he  found  on  the  island — viz.,  a  moth,  several  flies,  and  numerous 
beetles — he  found  to  be  incapable  of  flight;  and  therefore,  as  Wallace 
observes,  "as  these  insects  could  hardly  have  reached  the  islands  in 
a  wingless  state,  even  if  there  were  any  other  known  land  inhabited 
by  them,  which  there  is  not,  we  must  assume  that,  like  the  Madeiran 
insects,  they  were  originally  winged,  and  lost  their  power  of  flight 
because  its  possession  was  injurious  to  them" — Kerguelen  Island 
being  "  one  of  the  stormiest  places  on  the  globe, "  and  therefore  a  place 
where  insects  could  rarely  afford  to  fly  without  incurring  the  danger 
of  being  blown  out  to  sea. 

Here  is  another  and  perhaps  an  even  more  suggestive  class  of 
facts. 


144      READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

It  is  now  many  years  ago  since  the  editors  of  Silliman's  Journal 
requested  the  late  Professor  Agassiz  to  give  them  his  opinion  on  the 
following  question.  In  a  certain  dark  subterranean  cave,  called  the 
Mammoth  Cave,  there  are  found  some  peculiar  species  of  blind  fishes. 
Now  the  editors  of  Silliman's  Journal  wished  to  know  whether  Profes- 
sor Agassiz  would  hold  that  these  fish  had  been  specially  created  in 
these  caves,  and  purposely  devoided  of  eyes  which  could  never  be  of 
any  use  to  them;  or  whether  he  would  allow  that  these  fish  had  prob- 
ably descended  from  other  species,  but,  having  got  into  the  dark  cave, 
gradually  lost  their  eyes  through  disuse.  Professor  Agassiz,  who  was 
a  believer  in  special  creation,  allowed  that  this  ought  to  constitute 
a  crucial  test  as  between  the  two  theories  of  special  design  and  heredi- 
tary descent.  "If  physical  circumstances,"  he  said,  "ever  modified 
organised  human  beings,  it  should  be  easily  ascertained  here."  And 
eventually  he  gave  it  as  his  opinion,  that  these  fish  "were  created 
under  the  circumstances  in  which  they  now  live,  within  the  limits  over 
which  they  now  range,  and  with  the  structural  peculiarities  which  now 
characterise  them." 

Since  then  a  great  deal  of  attention  has  been  paid  to  the  fauna  of 
this  Mammoth  cave,  and  also  to  the  faunas  of  other  dark  caverns,  not 
only  in  the  New,  but  also  in  the  Old  World.  In  the  result,  the 
following  general  facts  have  been  fully  established. 

1.  Not  only  fish,  but  many  representatives  of  other  classes,  have 
been  found  in  dark  caves. 

2.  Wherever  the  caves  are  totally  dark,  all  the  animals  are  blind. 

3.  If  the  animals  live  near  enough  to  the  entrance  to  receive  some 
degree  of  light,  they  may  have  large  and  lustrous  eyes. 

4.  In  all  cases  the  species  of  blind  animals  are  closely  allied  to 
species  inhabiting  the  district  where  the  caves  occur;  so  that  the 
blind  species  inhabiting  the  American  caves  are  closely  allied  to 
American  species,  while  those  inhabiting  European  caves  are  closely 
allied  to  European  species. 

5.  In  nearly  all  cases  structural  remnants  of  eyes  admit  of  being 
detected,  in  various  degrees  of  obsolescence.  In  the  case  of  some  of 
the  crustaceans  of  the  Mammoth  cave  the  foot-stalks  of  the  eyes  are 
present,  although  the  eyes  themselves  are  entirely  absent. 

Now,  it  is  evident  that  all  these  general  facts  are  in  full  agreement 
with  the  theory  of  evolution,  while  they  offer  serious  difficulties  to 
the  theory  of  special  creation.  As  Darwin  remarks,  it  is  hard  to 
imagine  conditions  of  Ufe  more  similar  than  those  furnished  by  deep 


EVIDENCES  FROM  MORPHOLOGY 


145 


limestone  caverns  under  nearly  the  same  climate  in  the  two  continents 
of  America  and  Europe;  so  that,  in  accordance  with  the  theor>^  of 
special  creation,  very  close  similarity  in  the  organizations  of  the  two 
sets  of  faunas  might  have  been  expected.  But,  instead  of  this,  the 
affinities  of  these  two  sets  of  faunas  are  with  those  of  their  respective 
continents — as  of  course  they  ought  to  be  on  the  theory  of  evolution. 
Again,  what  would  have  been  the  sense  of  creating  the  useless  foot- 
stalks for  the  imaginary  support  of  absent  eyes,  not  to  mention  all  the 
other  various  grades  of  degeneration  in  other  cases  ?  So  that,  upon 
the  whole,  if  we  agree  with  the  late  Professor  Agassiz  in  regarding 
these  cave  animals  as  furnishing  a  crucial  test  between  the  rival 
theories  of  creation  and  evolution,  we  must  further  conclude  that  the 
whole  body  of  evidence  which  they  now  furnish  is  weighing  on  the 
side  of  evolution. 

So  much,  then,  for  a  few  special  instances  of  what  Darwin  called 
rudimentary  structures,  but  what  may  be  more  descriptively  desig- 
nated— in  accordance  with  the  theory  of  descent — obsolescent  or 
vestigial  structures.  It  is,  however,  of  great  importance  to  add  that 
these  structures  are  of  such  general  occurrence  throughout  both  the 
vegetable  and  animal  kingdoms  that,  as  Darwin  has  observed,  it  is 
almost  impossible  to  point  to  a  single  species  which  does  not  present 
one  or  more  of  them.  In  other  words,  it  is  almost  impossible  to  find 
a  single  species  which  does  not  in  this  way  bear  some  record  of  its  own 
descent  from  other  species;  and  the  more  closely  the  structure  of  any 
species  is  examined  anatomically,  the  more  numerous  are  such  records 
found  to  be.  Thus,  for  example,  of  all  organisms  that  of  man  has 
been  most  minutely  investigated  by  anatomists;  and  therefore  I  think 
it  will  be  instructive  to  conclude  this  chapter  by  giving  a  list  of  the 
more  noteworthy  vestigial  structures  which  are  known  to  occur  in  the 
human  body.  I  will  take  only  those  which  are  found  in  adult  man, 
reserving  for  the  next  chapter  those  which  occur  in  a  transitory  manner 
during  earlier  periods  of  his  Hfe.  But,  even  as  thus  restricted,  the 
number  of  obsolescent  structures  which  we  all  present  in  our  own 
person  is  so  remarkable,  that  their  combined  testimony  to  our  descent 
from  a  quadrumanous  ancestry  appears  to  me  in  itself  conclusive. 
I  mean,  that  even  if  these  structures  stood  alone,  or  apart  from  any 
more  general  evidences  of  our  family  relationships,  they  would  be 
sufficient  to  prove  our  parentage.  Nevertheless,  it  is  desirable  to 
remark  that  of  course  these  special  evidences  which  I  am  about  to 
detail  do  not  stand  alone.     Not  only  is  there  the  general  analogy 


146      READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

furnished  by  the  general  proof  of  evolution  elsewhere,  but  there  is 
likewise  the  more  special  correspondence  between  the  whole  of  our 
anatomy  and  that  of  our  nearest  zoological  allies.  Now  the  force  of 
this  latter  consideration  is  so  enormous  that  no  one  who  has  not 
studied  human  anatomy  can  be  in  a  position  to  appreciate  it.  For 
without  special  study  it  is  impossible  to  form  any  adequate  idea  of  the 
intricacy  of  structure  which  is  presented  by  the  human  form.  Yet  it 
is  found  that  this  enormously  intricate  organisation  is  repeated  in  all 
its  details  in  the  bodies  of  the  higher  apes.  There  is  no  bone,  muscle, 
nerve,  or  vessel  of  any  importance  in  the  one  which  is  not  answered 
to  by  the  other.  Hence  there  are  hundreds  of  thousands  of  instances 
of  the  most  detailed  correspondence,  without  there  being  any  instances 
to  the  contrary,  if  we  pay  due  regard  to  vestigial  characters.  The 
entire  corporeal  structure  of  man  is  an  exact  anatomical  copy  of  that 
which  we  find  in  the  ape. 

My  object,  then,  here  is  to  limit  attention  to  those  features  of  our 
corporeal  structure  which,  having  become  useless  on  account  of  our 
change  in  attitude  and  habits,  are  in  the  process  of  becoming  obsolete, 
and  therefore  occur  as  mere  vestigial  records  of  a  former  state  of 
things.  For  example,  throughout  the  vertebrated  series,  from  fish 
to  mammals,  there  occurs  in  the  inner  corner  of  the  eye  a  semi- 
transparent  eye-lid,  which  is  called  the  nictitating  membrane.  The 
object  of  this  structure  is  to  sweep  rapidly,  every  now  and  then, 
over  the  external  surface  of  the  eye,  apparently  in  order  to  keep  the 
surface  clean.  But  although  the  membrane  occurs  in  all  classes  of 
the  sub-kingdom,  it  is  more  prevalent  in  some  than  in  others — e.g., 
in  birds  than  in  mammals.  Even,  however,  where  it  does  not  occur 
of  a  size  and  mobility  to  be  of  any  use,  it  is  usually  represented,  in 
animals  above  fishes,  by  a  functionless  rudiment,  as  here  depicted  in 
the  case  of  man  (Fig.  19). 

Now  the  organisation  of  man  presents  so  many  vestigial  structures 
thus  referring  to  various  stages  of  his  long  ancestral  history,  that  it 
would  be  tedious  so  much  as  to  enumerate  them.  Therefore  I  will 
yet  further  limit  the  list  of  vestigial  structures  to  be  given  as  examples, 
by  not  only  restricting  these  to  cases  which  occur  in  our  own  organisa- 
l^ion;  but  of  them  I  shall  mention  only  such  as  refer  us  to  the  very 
last  stage  of  our  ancestral  history — viz.,  structures  which  have  become 
obsolescent  since  the  time  when  our  distinctively  human  branch  of 
the  family  tree  diverged  from  that  of  our  immediate  forefathers,  the 
Quadrumana. 


EVIDENCES  FROM  MORPHOLOGY 


147 


J^/^X 


JMf^pT 


Fig.  19. — Illustrations  of  the  nictitating  membrane  in  the  various  animals 
named,  drawn  from  nature.  The  letter  N  indicates  the  membrane  in  each  case. 
In  man  it  is  called  the  plica  semilunaris  and  is  represented  in  the  two  lower  drawings 
under  this  name.  In  the  case  of  the  shark  {Galeus),  the  muscular  membrane  is 
shown  as  dissected.     {From  Romanes.) 


148      READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

I.  Muscles  of  the  external  ear. — These,  which  are  of  large  size 
and  functional  use  in  quadrupeds,  we  retain  in  a  dwindled  and  useless 
condition  (Fig.  20).  This  is  likewise  the  case  in  anthropoid  apes; 
but  in  not  a  few  other  Quadrumana  (e.  g.,  baboons,  macacus,  magots^ 
etc.)  degeneration  has  not  proceeded  so  far,  and  the  ears  are 
voluntarily  movable. 


Fig.  20. — Rudimentary,  or  vestigial  and  useless,  muscles  of  the  human  ear. 
{From  Romanes,  after  Gray) 

2.  Panniculus  carnosis. — A  large  number  of  the  mammalia  are 
able  to  move  their  skin  by  means  of  subcutaneous  muscle,  as  we  see, 
for  instance,  in  a  horse,  when  thus  protecting  himself  against  the 
sucking  of  flies.  We,  in  common  with  the  Quadrumana,  possess  an 
active  remnant  of  such  a  muscle  in  the  skin  of  the  forehead,  whereby 
we  draw  up  the  eyebrows;  but  we  are  no  longer  able  to  use  other 
considerable  remnants  of  it,  in  the  scalp  and  elsewhere, — or  more 
correctly  it  is  rarely  that  we  meet  with  persons  who.  can.  But  most 
of  the  Quadrumana  (including  the  anthropoids)  are  still  able  to  do  so. 


EVIDENCES  FROM  :\IORPHOLOGY 


149 


There  are  also  many  other  vestigial  muscles,  which  occur  only  in  a 
small  percentage  of  human  beings,  but  which,  when  they  do  occur, 
present  unmistakable  homologies  with  normal  muscles  in  some  of 
the  Quadrumana  and  still  lower  animals. 

3.  Feet. — It  is  observable  that  in  the  infant  the  feet  have  a 
strong  reflection  inwards,  so  that  the  soles  in  considerable  measure 
face  one  another.  This  peculiarity,  which  is  even  more  marked  in 
the  embryo  than  in  the  infant,  and  which  becomes  gradually  less  and 


Fig.  21. — Portrait  of  a  young  gorilla.     {From  Romanes,  after  Hartmann.) 


less  conspicuous  even  before  the  child  begins  to  walk,  appears  to  me 
a  highly  suggestive  peculiarity.  For  it  plainly  refers  to  the  condition 
of  things  in  the  Quadrumana,  seeing  that  in  all  these  animals  the  feet 
are  similarly  curved  inwards,  to  facilitate  the  grasping  of  branches. 
And  even  when  walking  on  the  ground  apes  and  monkeys  employ  to 
a  great  extent  the  outside  edges  of  their  feet,  as  does  also  a  child  when 
learning  to  walk.  The  feet  of  a  young  child  are  also  extraordinarily 
mobile  in  all  directions,  as  are  those  of  apes.  In  order  to  show  these 
points,  I  here  introduce  comparative  drawings  of  a  young  ape  and  the 


150     READINGS  IN  EVOLUTION,   GENETICS,  AND  EUGENICS 

lower  extremities  of  a  still  younger  child.  These  drawings,  moreover, 
serve  at  the  same  time  to  illustrate  two  other  vestigial  characters, 
which  have  often  been  previously  noticed  with  regard  to  the  infant's 
foot.  I  allude  to  the  incurved  form  of  the  legs  and  the  lateral  exten- 
sion of  the  great  toe,  whereby  it  approaches  the  thumb-like  character 
of  this  organ  in  the  Quadrumana.  As  in  the  case  of  the  incurved 
position  of  the  legs  and  feet,  so  in  this  case  of  the  lateral  extensibility 
of  the  great  toe,  the  peculiarity  is  even  more  marked  in  embryonic 


Fig.  22. — Lower  extremities  of  a  young  child.  Drawn  from  life,  when  the 
mobile  feet  were  for  a  short  time  at  rest  in  a  position  of  extreme  inflection.  {From 
Romanes.) 


than  in  infant  life.  For,  as  Professor  Wyman  has  remarked  with 
regard  to  the  foetus  when  about  an  inch  in  length,  ''The  great  toe  is 
shorter  than  the  others;  and,  instead  of  being  parallel  to  them,  is 
projected  at  an  angle  from  the  side  of  the  foot,  thus  corresponding 
with  the  permanent  condition  of  this  part  in  the  Quadrumana."  So 
that  this  organ,  which,  according  to  Owen,  "is  perhaps  the  most 
characteristic  peculiarity  of  the  human  structure,"  when  traced  back 
to  the  early  stages  of  its  development,  is  found  to  present  a  notably 
less  degree  of  peculiarity. 


EVIDENCES  FROM  MORPHOLOGY 


151 


4.  Hands. — Dr.  Louis  Robinson  has  recently  observed  that  the 
grasping  power  of  the  whole  human  hand  is  so  surprisingly  great  at 
birth,  and  during  the  first  few  weeks  of  infancy,  as  to  be  far  in  excess 
of  present  requirements  on  the  part  of  a  young  child.  Hence  he  con- 
cludes that  it  refers  us  to  our  quadrumanous  ancestry — the  young  of 
anthropoid  apes  being  endowed  with  similar  powers  of  grasping,  in 
order  to  hold  on  to  the  hair  of  the  mother  when  she  is  using  her  arms  for 
the  purposes  of  locomotion.     This  inference  appears  to  me  justifiable, 


Fig.  23. — An  infant,  three  weeks  old,  supporting  its  own  weight  for  over  two 
minutes.  The  attitude  of  the  lower  limbs,  feet,  toes,  is  strikingly  simian.  Repro- 
duced from  an  instantaneous  photograph,  kindly  given  for  the  purpose  by  Dr.  L. 
Robinson.     {From  Romanes.) 


inasmuch  as  no  other  explanation  can  be  given  of  the  comparatively 
inordinate  muscular  force  of  an  infant's  grip.  For  experiments 
showed  that  very  young  babies  are  able  to  support  their  own  weight, 
by  holding  on  to  a  horizontal  bar,  for  a  period  varying  from  one 
half  to  more  than  two  minutes.  With  his  kind  permission,  I  here 
reproduce  one  of  Dr.  Robinson's  instantaneous,  and  hitherto  unpub- 
lished, photographs  of  a  very  young  infant.  This  photograph  was 
taken  after  the  above  paragraph  (3)  was  written,  and  I  introduce  it 
here  because  it  serves  to  show  incidentally— and  perhaps  even  better 
than  the  preceding  figure— the  points  there  mentioned  with  regard 


152      READINGS  IN  EVOLUTION,  GExNETICS,  AND  EUGENICS 

to  the  feet  and  great  toes.  Again,  as  Dr.  Robinson  observes,  the 
attitude,  and  the  disproportionately  large  development  of  the  arms 
as  compared  with  the  legs  give  all  the  photographs  a  striking  resem- 
blance to  a  picture  of  the  chimpanzee  ''Sally"  at  the  Zoological 
Gardens.  For  "  invariably  the  thighs  are  bent  nearly  at  right  angles 
to  the  body,  and  in  no  case  did  the  lower  limbs  hang  down  and  take 
the  attitude  of  the  erect  position."  He  adds,  ''In  many  cases  no 
sign  of  distress  is  evinced,  and  no  cry  uttered,  until  the  grasp 
begins  to  give  way." 


MAN 


Gorilla 


Fig.  24. — Sacrum  of  gorilla  compared  with  that  of  man,  showing  rudimentary 
tail  bones  of  each.     Drawn  from  nature.     (From  Romanes.) 


5.  Tail. — The  absence  of  a  tail  in  man  is  popularly  supposed  to 
constitute  a  difficulty  against  the  doctrine  of  his  quadrumanous 
descent.  As  a  matter  of  fact,  however,  the  absence  of  an  external 
tail  in  man  is  precisely  what  this  doctrine  would  expect,  seeing  that 
the  nearest  allies  of  man  in  the  quadrumanous  series  are  likewise 
destitute  of  an  external  tail.  Far,  then,  from  this  deficiency  in  man 
constituting  any  difficulty  to  be  accounted  for,  if  the  case  were  not 
so — i.e.,  if  man  did  possess  an  external  tail, — the  difficulty  would  be 
to  understand  how  he  had  managed  to  retain  an  organ  which  had  been 
renounced  by  his  most  recent  ancestors.     Nevertheless,  as  the  anthro- 


EVIDENCES  FROM  MORPHOLOGY 


153 


poid  apes  continue  to  present  the  rudimentary  vestiges  of  a  tail  in  a 
few  caudal  vertebrae  below  the  integuments,  we  might  well  expect  to 
find  a  similar  state  of  matters  in  the  case  of  man.     And  this  is  just 


Fig.  25. — Diagrammatic  outline  of  the  human  embryo  when  about  seven 
weeks  old,  showing  the  relations  of  the  limbs  and  tail  to  the  trunk,  (After  Allen 
Thompson.)  r,  the  radial,  and  n,  the  ulnar,  border  of  the  hand  and  forearm; 
t,  the  tibial,  and/  the  fibular,  border  of  the  foot  and  lower  leg;  ati,  ear;  s,  spinal 
cord;  v,  umbilical  cord;  b,  bronchial  gill  slits;  c,  tail.     (From  Romanes.) 


S\ifj\^-s>]/o\Js  be 


dvf^roHf^  dotc/di^  fc 


^  ^     Lid. 


fosr.sjtkp-docM 

Z./C 


Fig.  26. — Front  and  back  view  of  adult  human  sacrum,  showing  abnormal 
persistence  of  vestigial  tail  muscles.     (From  Romanes.) 


what  we  do  find,  as  a  glance  at  these  two  comparative  illustrations 
will  show  (Fig.  24).  Moreover,  during  embryonic  life,  both  of  the 
anthropoid  apes  and  of  man,  the  tail  much  more  closely  resembles 


154      READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

that  of  the  lower  kinds  of  quadrumanous  animals  from  which  these 
higher  representatives  of  the  group  have  descended.  For  at  a  certain 
stage  of  embryonic  life  the  tail,  both  of  apes  and  of  human  beings,  is 


Fig.  27. — Appendix  vermiformis  in  orang  and  in  man,  //,  ilium;  Co,  colon; 
C,  coecum;  [F,  a  window  cut  in  the  wall  of  the  coecum;  ^a;^;,  the  appendix.  {From 
Romanes.) 


Man 
F(ETAL 


Fig.  28. — The  same,  showing  variation  in  the  orang.     {From  Romanes.) 


actually  longer  than  the  legs  (see  Fig.  25).  And  at  this  stage  of 
development,  also,  the  tail  admits  of  being  moved  by  muscles  which 
later  on  dwindle  away.  Occasionally,  however,  these  muscles  persist, 
and  are  then  described  by  anatomists  as  abnormalities.     The  illustra- 


EVIDENCES  FROM  MORPHOLOGY 


155 


tions  on  page  153  (Fig.  26)  serve  to  show  the  muscles  in  question, 
when  thus  found  in  adult  man. 

6.  Vermiform  appendix  of  the  coecum. — This  is  of  large  size  and 
functional  use  in  the  process  of  digestion  among  many  herbivorous 
animals;  while  in  man  it  is  not  only  too  small  to  serve  any  such 
purpose,  but  is  even  a  source  of  danger  to  life — many  persons  dying 
every  year  from  inflammation  set  up  by  the  lodgement  in  this  blind 
tube  of  fruit-stones,  etc. 

In  the  orang  it  is  longer  than  in  man  (Fig.  27),  as  it  is  also  in  the 
human  foetus  proportionally  compared  with  the  adult  (Fig.  28).  In 
some  of  the  lower  herbivorous  animals  it  is  longer  than  the  entire  body. 

Like  the  vestigial  structures  in  general,  however,  this  one  is 
highly  variable.  Thus  Figure  28  serves  to  show  that  it  may  some- 
times be  almost  as  short  in  the  orang  as  it  normally  is  in  man — both 
the  human  subjects  of  this  illustration  having  been  normal. 

7.  Ear. — Mr.  Darwin  writes: 

^'The  celebrated  sculptor,  Mr.  Woolner,  informs  me  of  one  little 
peculiarity  in  the  external  ear,  which  he  has  often  observed  both  in 

men  and  women The  peculiarity  consists  in  a  little  blunt 

point,  projecting  from  the  inwardly  folded  margin,  or  helix.  When 
present,  it  is  developed  at  birth,  and  according  to  Professor  Ludwig 
Meyer,  more  frequently  in  man  than  in  woman. 
Mr.  Woolner  made  an  exact  model  of  one  such 
case,  and  sent  me  the  accompanying  draw- 
ing [Fig.  29] The  helix  obviously  con- 
sists of  the  extreme  margin  of  the  ear  folded 
inwards;  and  the  folding  appears  to  be  in  /f^ 
some  manner  connected  with  the  whole  external 
ear  being  permanently  pressed  backwards.  In 
many  monkeys,  which  do  not  stand  high  in 
the  order  as  baboons  and  some  species  of 
macacus,  the  upper  portion  of  the  ear  is  slightly 
pointed,  and  the  margin  is  not  at  all  folded 
inwards;  but  if  the  margin  were  to  be  thus 
folded,  a  slight  point  would  necessarily  pro- 
ject towards  the  centre In  Figure  30 

is  shown  an  accurate  copy  of  a  photograph 

of  the  foetus  of  an  orang  (kindly  sent  me  by  Dr.  Nitsche),  in 
which  it  may  be  seen  how  different  the  ])oinled  outhne  of  the  car  is 
at  this  period  from  its  adult  condition,  when  it  bears  a  close  general 


Fig.  29. — Human  ear, 
modeled  and  drawn  by 
Mr.  Woolner.  a,  the  pro- 
jecting point.  {From  Ro- 
manes.) 


156      READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 


Fig.  30. — Foetus  of  an  ©rang.  Exact 
copy  of  a  photograph,  showing  the  form  of 
ear  at  this  early  stage.     {From  Romanes.) 


resemblance  to  that  of  man  (including  even  the  occasional  appear- 
ance of  the  projecting  point  shown  in  the  preceding  woodcut).     It  is 

evident  that  the  folding  over 
of  the  tip  of  such  an  ear, 
unless  it  is  changed  greatly 
during  its  further  develop- 
ment, would  give  rise  to  a 
point  projecting  inwards."' 

The  woodcut  on  page  157 
(Fig.  31)  serves  still  further  to 
show  vestigial  resemblances 
between  the  human  ear  and 
that  of  apes.  The  last  two 
figures  illustrate  the  general 
resemblance  between  the  nor- 
mal ear  of  foetal  man  and  the 
ear  of  an  adult  orangoutang. 
The  other  two  figures  on  the 
lower  line  are  intended  to 
exhibit  occasional  modifica- 
tions of  the  adult  human  ear,  which  approximate  simian  characters 
somewhat  more  closely  than  does  the  normal  type.  It  will  be  observed 
that  in  their  comparatively  small  lobes  these  ears  resemble  those 
of  all  the  apes;  and  that  while  the  outer  margin  of  one  is  not  unlike 
that  of  the  Barbary  ape,  the  outer  margin  of  the  other  follows  those 
of  the  chimpanzee  and  orang.  Of  course  it  would  be  easy  to  select 
individual  human  ears  which  present  either  of  these  characters  in  a 
more  pronounced  degree;  but  these  ears  have  been  chosen  as  models 
because  they  present  both  characters  in  conjunction.  The  upper  row 
of  figures  likewise  shows  the  close  similarity  of  hair-tracts,  and  the 
direction  of  growth  on  the  part  of  the  hair  itself,  in  cases  where  the 
human  hair  happens  to  be  of  an  abnormally  hirsute  character.  But 
this  particular  instance  (which  I  do  not  think  has  been  previously 
noticed)  introduces  us  to  the  subject  of  hair,  and  hair-growth,  in 
general. 

8.  Hair. — Adult  man  presents  rudimentary  hairs  over  most  parts 
of  the  body.  Wallace  has  sought  to  draw  a  refined  distinction  between 
this  vestigial  coating  and  the  useful  coating  of  quadrumanous 
animals,  in  the  absence  of  the  former  from  the  human  back.     But  even 

^  Descent  of  Man  (2d  ed.),  pp.  15-16. 


EVIDENCES  FROM  MORPHOLOGY 


157 


c^ 


o 
i-i 

3 
•_> 

C 


C 

o 

Ui 


e4 


en 


3 


(J 

u 


v:       *Sb 


fO 


O 


158     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

this  refined  distinction  does  not  hold.  On  the  one  hand,  the  com- 
paratively hairless  chimpanzee  which  died  last  year  in  the  Zoological 
Gardens  {T.  calvus)  was  remarkably  denuded  over  the  back;  and,  on 
the  other  hand,  men  who  present  a  considerable  development  of  hair 
over  the  rest  of  their  bodies  present  it  also  on  their  backs  and  shoul- 
ders. Again,  in  all  men  the  rudimentary  hair  on  the  upper  and  lower 
arm  is  directed  towards  the  elbow — a  peculiarity  which  occurs  nowhere 
else  in  the  animal  kingdom,  with  the  exception  of  the  anthropoid  apes 
and  a  few  American  monkeys,-  where  it  presumably  has  to  do  with 
arboreal  habits.  For,  when  sitting  in  trees,  the  orang,  as  observed  by 
Mr.  Wallace,  places  its  hands  above  its  head  with  its  elbows  pointing 
downwards;  the  disposition  of  hair  on  the  arms  and  fore-arms  then 
has  the  effect  of  thatch  in  turning  the  rain.  Again,  I  find  that  in  all 
species  of  apes,  monkeys,  and  baboons  which  I  have  examined  (and 
they  have  been  numerous),  the  hair  on  the  backs  of  the  hands  and  feet 
is  continued  as  far  as  the  first  row  of  phalanges;  but  becomes  scanty, 
or  disappears  altogether,  on  the  second  row;  while  it  is  invariably 
absent  on  the  terminal  row.  I  also  find  that  the  same  peculiarity 
occurs  in  man.  We  all  have  rudimentary  hair  on  the  first  row  of 
phalanges,  both  of  hands  and  feet:  when  present  at  all,  it  is  more 
scanty  on  the  second  row;  and  in  no  case  have  I  been  able  to  find  any 
on  the  terminal  row.  In  all  cases  these  peculiarities  are  congenital, 
and  the  total  absence  or  partial  presence  of  hair  on  the  second  pha- 
langes is  constant  in  different  species  of  Quadrumana.  For  instance , 
it  is  entirely  absent  in  all  the  chimpanzees,  which  I  have  examined, 
while  scantily  present  in  all  the  orangs.  As  in  man,  it  occurs  in  a 
patch  midway  between  the  joints. 

Besides  showing  these  two  features  with  regard  to  disposition  of  hair 
on  the  human  arm  and  hand,  the  woodcut  on  page  159  (Fig.  32)  illustrates 
a  third.  By  looking  closely  at  the  arm  of  the  very  hairy  man  from  whom 
the  drawing  was  taken,  it  could  be  seen  that  there  was  a  strong  tendency 
towards  a  whorled  arrangement  of  the  hairs  on  the  backs  of  the  wrists. 
This  is  likewise,  as  a  general  rule,  a  marked  feature  in  the  arrangement 
of  hair  on  the  same  places  in  the  gorilla,  orang,  and  chimpanzee.  In 
the  specimen  of  the  latter,  however,  from  which  the  drawing  was  taken 
this  characteristic  was  not  well  marked.  The  downward  direction  of 
the  hair  on  the  backs  of  the  hands  is  exactly  the  same  in  man  as  it  is 
in  all  the  anthropoid  apes.  Again,  with  regard  to  hair,  Darwin 
notices  that  occasionally  there  appears  in  man  a  few  hairs  in  the  eye- 
brows much  longer  than  the  others;    and  that   they   seem   to  be 


EVIDENCES  FROM  MORPHOLOGY 


159 


y^f/KL  t  CM'Mf^^^^^* 


Fig.  32. — Hair  tracts  on  the  arms  and  hands  of  man,  as  compared  with  those 
of  the  chimpanzee.     Drawn  from  Hfe.     {From  Romanes.) 


i6o     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

representative  of  similarly  long  and  scattered  hairs  which  occur 
in  the  chimpanzee,  macacus,  and  baboons. 

Lastly,  it  may  be  here  more  conveniently  observed  than  in  the 
next  chapter  on  Embryology,  that  at  about  the  sixth  month  the  human 
foetus  is  often  thickly  coated  with  somewhat  long  dark  hair  over  the 
entire  body,  except  the  soles  of  the  feet  and  palms  of  the  hands,  which 
are  likewise  bare  in  all  quadrumanous  animals.  This  covering,  which 
is  called  the  lanugo,  and  sometimes  extends  even  to  the  whole  fore- 
head, ears,  and  face,  is  shed  before  birth.  So  that  it  appears  to  be 
useless  for  any  purpose  other  than  that  of  emphatically  declaring  man 
a  child  of  the  monkey. 

9.  Teeth. — Darwin  writes: 

"It  appears  as  if  the  posterior  molar  or  wisdom  teeth  were  tending 
to  become  rudimentary  in  the  more  civilized  races  of  man.  These 
teeth  are  rather  smaller  than  the  other  molars,  as  is  likewise  the  case 
with  the  corresponding  teeth  in  the  chimpanzee  and  orang;  and  they 

have  only  two  separate  fangs They  are  also  much  more  liable 

to  vary,  both  in  structure  and  in  the  period  of  their  development, 
than  the  other  teeth.  In  the  Melanian  races,  on  the  other  hand,  the 
wisdom-teeth  are  usually  furnished  with  three  separate  fangs,  and  are 
usually  sound  (i.e.,  not  specially  liable  to  decay);  they  also  differ  from 
the  other  molars  in  size,  less  than  in  the  Caucasian  races." 

Now,  in  addition  to  these  there  are  other  respects  in  which  the 
dwindling  condition  of  wisdom-teeth  is  manifested — particularly  with 
regard  to  the  pattern  of  their  crowns.  Indeed,  in  this  respect  it  would 
seem  that  even  in  the  anthropoid  apes  there  is  the  beginning  of  a 
tendency  to  degeneration  of  the  molar  teeth  from  behind  forwards. 
For  if  we  compare  the  three  molars  in  the  lower  jaw  of  the  gorilla, 
orang,  and  chimpanzee,  we  find  that  the  gorilla  has  five  well-marked 
cusps  on  all  three  of  them;  but  that  in  the  orang  the  cusps  are  not  so 
pronounced,  while  in  the  chimpanzee  there  are  only  four  of  them  on 
the  third  molar.  Now  in  man  it  is  only  the  first  of  these  three  teeth 
which  normally  presents  five  cusps,  both  the  others  presenting  only 
four.  So  that,  comparing  all  these  genera  together,  it  appears  that 
the  number  of  cusps  is  being  reduced  from  behind  forwards;  the 
chimpanzee  having  lost  one  of  them  from  the  third  molar,  while  man 
has  not  only  lost  this,  but  also  one  from  the  second  molar, — and  it 
may  be  added,  likewise  partially  (or  even  totally)  from  the  first  molar, 
as  a  frequent  variation  among  civilized  races.  But,  on  the  other  hand, 
variations  are  often  met  with  in  the  opposite  direction,  where  the 


EVIDENCES  FROM  MORPHOLOGY 


i6i 


second  or  the  third  molar  of  man  presents  five  cusps — in  the  one  case 
following  the  chimpanzee,  in  the  other  the  gorilla.  These  latter  varia- 
tions, therefore,  may  fairly  be  regarded  as  reversionary.  For  these 
facts  I  am  indebted  to  the  kindness  of  Mr.  C.  S.  Tomes. 

10.  Perforations  of  the  humerus. — The  peculiarities  which  we 
have  to  notice  under  this  heading  are  two  in  number.  First,  the 
supra-condyloid  foramen  is  a  normal  feature  in  some  of  the  lower 
Quadrumana  (Fig.  34),  where  it  gives  passage  to  the  great  nerve  of 


/^aK. 


Fig.  33. — Molar  teeth  of  lower  jaw  in  gorilla,  orang,  and  man.     Drawn  from 
nature,  nat.  size.     (From  Romanes.) 


the  forearm,  and  often  also  to  the  great  artery.  In  man,  however, 
it  is  not  a  normal  feature.  Yet  it  occurs  in  a  small  percentage  of 
cases — viz.,  according  to  Sir  W.  Turner,  in  about  one  per  cent,  and 
therefore  is  regarded  by  Darwin  as  a  vestigial  character.  Secondly, 
there  is  inter-condyloid  foramen,  which  is  also  situated  near  the  lower 
end  of  the  humerus,  but  more  in  the  middle  of  the  bone.  This  occurs, 
but  not  constantly,  in  apes,  and  also  in  the  human  species.  From 
the  fact  that  it  does  so  much  more  frequently  in  the  bones  of  ancient 
— and  also  of  some  savage — races  of  mankind  (viz.  in  20  to  30  per  cent 
of  cases),  Darwin  is  disposed  to  regard  it  also  as  a  vestigial  feature. 


l62      READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

On  the  other  hand,  Prof.  Flower  tells  me  that  in  his  opinion  it  is  but 
an  expression  of  impoverished  nutrition  during  the  growth  of  the  bone. 
II.  Flattening  of  Tibia. — In  some  very  ancient  human  skeletons 
there  has  also  been  found  a  lateral  flattening  of  the  tibia,  which  rarely 
occurs  in  any  existing  human  beings,  but  which  appears  to  have 
been  usual  among  the  earliest  races  of  mankind  hitherto  discovered. 
According  to  Broca,  the  measurements  of  these  fossil  human  tibiae 
resemble  those  of  apes.     Moreover,  the  bone  is  bent  and  strongly 


JAVAI7  LOR{S 


CAPWCHIi;. 


Fig.  34. — Perforations  of  the  humerus  (supra-condyloid  foramen)  in  three 
species  of  Quadrumana  where  it  normally  occurs,  and  in  man,  where  it  does  not 
normally  occur.     Drawn  from  nature.     {From  Romanes.) 


convex  forwards,  while  its  angles  are  so  rounded  as  to  present  the 
nearly  oval  section  seen  in  apes.  It  is  in  association  with  these 
ape-like  human  tibiae  that  perforated  humeri  of  man  are  found  in 
greatest  abundance. 

On  the  other  hand,  however,  there  is  reason  to  doubt  whether 
this  form  of  tibia  in  man  is  really  a  survival  from  his  quadrumanous 
ancestry.  For,  as  Boyd-Dawkins  and  Hartmann  have  pointed  out, 
the  degree  of  flattening  presented  by  some  of  these  ancient  human 
bones  is  greater  than  that  which  occurs  in  any  existing  species  of 
anthropoid  ape.  Of  course  the  possibility  remains  that  the  unknown 
species  of  ape  from  which  man  descended  may  have  had  its  tibia  more 
flattened  than  is  now  observable  in  any  of  the  existing  species.     Never- 


EVIDENCES  FROM  MORPHOLOGY  163 

theless,  as  some  doubt  attaches  to  this  particular  case,  I  do  not  press 
it — and,  indeed,  only  mention  it  at  all  in  order  that  the  doubt  may  be 
expressed. 

Similarly,  I  will  conclude  by  remarking  that  several  other  instances 
of  the  survival  of  vestigial  structures  in  man  have  been  alleged,  which 
are  of  a  still  more  doubtful  character.  Of  such,  for  example,  are  the 
supposed  absence  of  the  genial  tubercle  in  the  case  of  a  very  ancient 
jaw-bone  of  man,  and  the  disposition  of  valves  in  human  veins. 
From  the  former  it  was  argued  that  the  possessor  of  this  very  ancient 
jaw-bone  was  probably  speechless,  inasmuch  as  the  tubercle  in  existing 
man  gives  attachment  to  muscles  of  the  tongue.  From  the  latter  it 
has  been  argued  that  all  the  valves  in  the  veins  of  the  human  body 
have  reference,  in  their  disposition,  to  the  incidence  of  blood-pressure 
when  the  attitude  of  the  body  is  horizontal,  or  quadrupedal.  Now, 
the  former  case  has  already  broken  down,  and  I  find  that  the  latter 
does  not  hold.  But  we  can  well  afford  to  lose  such  doubtful  and 
spurious  cases,  in  view  of  all  the  foregoing  unquestionable  and  genuine 
cases  of  vestigial  structures  which  are  to  be  met  with  even  within  the 
limits  of  our  own  organization — and  even  when  these  limits  are  still 
further  limited  by  selecting  only  those  instances  which  refer  to  the 
very  latest  chapter  of  our  long  ancestral  history. 


CHAPTER  XI 
EVIDENCES  FROM  EMBRYOLOGY 

THE  FACTS  OF  REPRODUCTION  AND  DEVELOPMENT 

[It  is  now  definitely  known  that  all  living  creatures  are  mortal,  at 
least  as  individuals,  but  they  all  have  the  capacity  of  continuing  their 
life  by  the  reproduction  of  offspring.  This  physical  immortality  is 
based  upon  an  actual  transmission  from  parent  to  offspring  of  some 
material  substance  which  is  so  organized  chemically  as  to  be  fully 
representative  of  the  race  or  stock  to  which  the  parent  belongs. 

Reproduction  may  be  asexual  or  sexual.  In  asexual  development 
a  new  individual  may  be  produced  by  a  process  oi  fission  (dividing  the 
parent  into  two  or  more  parts,  each  of  which  has  the  capacity  to 
develop  into  a  whole  new  individual) ;  by  budding  (the  production  of 
new  individuals  by  means  of  outgrowths  of  the  parent-body) ;  or  by 
giving  off  spores  or  eggs  capable  of  development  without  fertiliza- 
tion (parthenogenesis).  In  sexual  reproduction  two  kinds  of  parent- 
individuals  exist:  one  a  female  which  is  capable  of  giving  off  relatively 
large  single  cells,  called  eggs  (ova) ;  and  the  other  a  male,  which  is 
capable  of  producing  minute,  usually  motile  cells,  called  spermatozoa. 
A  union  of  ovum  and  spermatozoon  is  usually  necessary  before  the 
ovum  can  begin  its  development.  It  is  the  sexual  method  of  repro- 
duction that  will  chiefly  concern  us  here,  and,  for  present  purposes,  we 
may  omit  any  further  mention  of  the  various  asexual  methods. 

An  ovum  may  be  conceived  of  as  an  individual  of  some  definite 
species  or  race  reduced  to  the  very  lowest  terms.  It  exhibits  the 
characteristic  cell  structure,  consisting  of  cytoplasm  and  nucleus,  cell 
membrane,  nuclear  membrane,  usually  a  centrosome  (Fig.  43). 
Further  details  as  to  the  minute  structure  of  the  nucleus  are  given  in 
chapter  xxvii,  where  the  mechanism  of  Mendelian  heredity  is  dealt 
with. — Ed.] 

''The  reproductive  cells  from  the  two  sexes,"  says  Wright,'  ''have 
very  different  appearances.  In  mammals,  the  ovum  is  a  relatively 
large,  spherical  cell,  just  visible  to  the  naked  eye. 

^  From  Sewall  Wright,  Principles  of  Livestock  Breeding,  United  States  Depart- 
ment of  Agriculture,  Bulletin  No.  905. 

164 


EVIDENCES  FROM  EMBRYOLOGY  165 

"In  birds,  the  yolk  of  an  egg  is  really  a  single  ovum,  distended  to 
an  enormous  size  by  food  material.  The  sperm  cell  is  very  much 
smaller  and  can  be  seen  well  only  with  a  high-power  microscope.  It  is 
something  like  a  tadpole  in  shape,  having  a  small  cell  body,  containing 
a  little  nucleus,  and  attached  to  this  a  long,  whiplike  process  which 
beats  rapidly  while  the  cell  is  alive,  enabling  it  to  seek  out  and  unite 
with  the  large  passive  egg  in  the  act  of  fertilization.  Enormous  num- 
bers of  sperm  cells  are  produced  by  the  male,  but  only  one  takes  part 
in  fertilization.  After  the  first  has  penetrated  the  membrane  of  an 
egg  cell,  a  change  takes  place  in  the  latter  which  prevents  the  entrance 
of  others. 

"The  sperm  activates  certain  formerly  inert  substances  in  the  egg 
and  the  new  combination  cell  (the  zygote)  starts  almost  at  once  to 
produce  a  new  individual." 

OUTLINE    OF   ANIMAL  DEVELOPMENT^ 
D,    S.    JORDAN   AND    V.    L.    KELLOGG 

The  embryonic  development  is  from  the  beginning  up  to  a  certain 
point  practically  alike,  looked  at  in  its  larger  aspect,  for  all  the  many- 
celled  animals.  That  is,  there  are  certain  principal  or  constant 
characteristics  of  the  beginning  development  which  are  present  in  the 
development  of  all  many-celled  animals.  The  first  stage  or  phenome- 
non of  development  is  the  simple  fission  of  the  germ  cell  into  halves 
(Fig.  35,  b).  These  two  daughter  cells  next  divide  so  that  there  are 
four  cells  (c) ;  each  of  these  divides,  and  this  division  is  repeated  until 
a  greater  or  lesser  number  (varying  with  the  various  species  or  groups 
of  animals)  of  cells  is  produced.  These  cells  may  not  all  be  of  the  same 
size,  but  in  many  cases  they  are,  no  structural  differentiation  whatever 
being  apparent  among  them. 

The  phenomenon  of  repeated  division  of  the  germ  cell  is  called 
cleavage,  and  this  cleavage  is  the  first  stage  of  development  in  the 
case  of  all  many-celled  animals.  The  germ  or  embryo  in  some  animals 
consists  now  of  a  mass  of  few  or  many  undifferentiated  primitive  cells 
lying  together  and  usually  forming  a  sphere  (Fig.  35,  e),  or  perhaps 
separated  and  scattered  through  the  food  yolk  of  the  egg.  The  next 
stage  of  development  is  this:  the  cleavage  cells  arrange  themselves  so 
as  to  form  a  usually  hollow  sphere  or  ball,  the  cells  lying  side  by  side  to 

*  From  D.  S.  Jordan  and  V.  L.  Kellogg,  Evolution  and  Animal  Life  (copyright 
1907).     Used  by  special  permission  of  the  publishers,  D.  Appleton  &  Company. 


1 66  ^READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

form  the  outer  circumferential  wall  of  this  hollow  sphere  (/).  This  is 
called'the  hlastiila  or  blastoderm  stage  of  development,  and  the  embryo 
itself  is  called  the  blastula  or  blastoderm.  This  stage  also  is  common 
to  all  the  many-celled  animals.  The  next  stage  in  embryonic  develop- 
ment is  formed  by  the  bending  inward  of  a  part  of  the  blastoderm  cell 
layer,  as  shown  in  (g)  (or  the  splitting  off  inwardly  of  cells  from  a 
special  part  of  the  blastula  cell  layer).  This  bending  in  may  produce 
a  small  depression  or  groove;  but  whatever  the  shape  or  extent  of  the 
sunken-in  part  of  the  blastoderm,  it  results  in  distinguishing  the 
blastoderm  layer  into  two  parts,  a  sunken-in  or  inner  portion  called 


Fig.  35. — First  stages  in  the  embryonic  development  of  the  pond  snail, 
Lymnaeus.  a,  egg  cell;  b,  first  cleavage;  c,  second  cleavage;  d,  third  cleavage; 
e,  after  numerous  cleavages;  /,  blastula — in  section;  g,  gastrula  just  forming — 
in  section;  h,  gastrula  completed — in  section.  (From  Jordan  and  Kellogg,  after 
Rabl.) 


the  endoblast  and  the  other  unmodified  portion  called  the  ectohlast. 
Endo-  means  within,  and  the  cells  of  the  endoblast  often  push  so  far 
into  the  original  blastoderm  cavity  as  to  come  into  contact  with  the 
cells  of  the  ectoblast  and  thus  obliterate  this  cavity  {h).  This  third 
well-marked  stage  in  the  embryonic  development  is  called  the  gastrula 
stage,  and  it  also  occurs  in  the  development  of  all  or  nearly  all  many- 
celled  animals. 

In  the  case  of  a  few  of  the  simple  many-celled  animals  the  embryo 
hatches — that  is,  issues  from  the  egg  at  the  time  of  or  very  soon  after 
reaching  the  gastrula  stage.  In  the  higher  animals,  however,  develop- 
ment goes  on  within  the  egg  or  within  the  body  of  the  mother  until 
the  embryo  becomes  a  complex  body,  composed  of   many  various 


EVIDENCES  FROM  EMBRYOLOGY  167 

tissues  and  organs.  Almost  all  the  development  may  take  place  within 
the  egg,  so  that  when  the  young  animal  hatches  there  is  necessary  little 
more  than  a  rapid  growth  and  increase  of  size  to  make  it  a  fully 
developed  mature  animal.  This  is  the  case  with  the  birds;  a  chicken 
just  hatched  has  most  of  the  tissues  and  organs  of  a  full-grown  fowl, 
and  is  simply  a  little  hen.  But  in  the  case  of  other  animals  the  young 
hatches  from  the  egg  before  it  has  reached  such  an  advanced  stage  of 
development;  a  young  starfish  or  young  crab  or  young  honeybee  just 
hatched  looks  very  different  from  its  parent.  It  has  yet  a  great  deal 
of  development  to  undergo  before  it  reaches  the  structural  condition 
of  a  fully  developed  and  fully  grown  starfish  or  crab  or  bee.  Thus 
the  development  of  some  animals  is  almost  wholly  embryonic  develop- 
ment— that  is,  development  within  the  egg  or  in  the  body  of  the 
mother — while  the  development  of  other  animals  is  largely  post- 
embryonic,  or  larval  development,  as  it  is  often  called.  There  is  no 
important  difference  between  embryonic  and  postembryonic  develop- 
ment. The  development  is  continuous  from  egg  cell  to  mature  animal, 
and  whether  inside  or  outside  of  an  egg  it  goes  on  regularly  and  uninter- 
ruptedly. 

The  cells  which  compose  the  embryo  in  the  cleavage  stage  and 
blastoderm  stage,  and  even  in  the  gastrula  stage,  are  apparently  all 
similar;  there  is  little  or  no  differentiation  shown  among  them.  But 
from  the  gastrula  stage  on,  development  includes  three  important 
things;  the  gradual  differentiation  of  cells  into  various  kinds  to  form 
the  various  kinds  of  animal  tissues;  the  arrangement  and  grouping 
of  these  cells  into  organs  and  body  parts;  and  finally  the  developing  of 
these  organs  and  body  parts  into  the  special  condition  characteristic 
of  the  species  of  animal  to  which  the  developing  individual  belongs. 
From  the  primitive  undifferentiated  cells  of  the  blastoderm,  develop- 
ment leads  to  the  special  cell  types  of  muscle  tissue,  of  bone  tissue,  of 
nerve  tissue;  and  from  the  generalized  condition  of  the  embryo  in  its 
early  stages,  development  leads  to  the  specialized  condition  of  the 
body  of  the  adult  animal.  Development  is  from  the  general  to  the 
special,  as  was  said  years  ago  by  von  Baer,  the  first  great  student  of 
development. 

A  starfish,  a  beetle,  a  dove,  and  a  horse  are  all  alike  in  their 
beginning — that  is,  the  body  of  each  is  composed  of  a  single  cell,  a 
single  structural  unit.  And  they  are  all  alike,  or  very  much  alike, 
through  several  stages  of  development;  the  body  of  each  is  first  a 
single  cell,  then  a  number  of  similar  undifferentiated  cells,  and  then  a 


1 68      READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

blastoderm  consisting  of  a  single  layer  of  similar  undifferentiated  cells. 
But  soon  in  the  course  of  development  the  embryo  begins  to  differ,  and 
as  the  young  animals  get  further  and  further  along  in  the  course  of 
their  development,  they  become  more  and  more  different  until  each 
finally  reaches  its  fully  developed  mature  form,  showing  all  the  great 
structural  differences  between  the  starfish  and  the  dove,  the  beetle  and 
the  horse.  That  is,  all  animals  begin  development  apparently  alike, 
but  gradually  diverge  from  each  other  during  the  course  of  develop- 
ment. 

There  are  some  extremely  interesting  and  significant  things  about 
this  divergence  to  which  attention  should  be  given.  While  all  animals 
are  apparently  alike  structurally  at  the  beginning  of  development,  so 
far  as  we  can  see,  they  do  not  all  differ  noticeably  at  the  time  of  the  first 
^divergence  in  development.  The  first  divergence  in  development  is  to 
be  noted  between  two  kinds  of  animals  which  belong  to  different  great 
groups  or  classes.  But  two  animals  of  different  kinds,  both  belonging 
to  some  one  great  group,  do  not  show  differences  until  later  in  their 
development.  This  can  best  be  understood  by  an  example.  All  the 
butterflies  and  beetles  and  grasshoppers  and  flies  belong  to  the  great 
group  or  class  of  animals  called  Insecta,  or  insects.  There  are  many 
different  kinds  of  insects,  and  these  kinds  can  be  arranged  in  subor- 
dinate groups  (orders),  such  as  the  Diptera,  or  flies,  the  Lepidoptera, 
or  butterflies  and  moths,  and  so  on.  But  all  have  certain  structural 
characteristics  in  common,  so  that  they  are  comprised  in  one  great 
class — the  Insecta.  Another  great  group  of  animals  is  known  as  the 
Vertebrata,  or  backboned  animals.  The  class  Vertebrata  includes  the 
fishes,  the  batrachians,  the  reptiles,  the  birds  and  the  mammals,  each 
composing  a  subordinate  group,  but  all  characterized  by  the  possession 
of  a  backbone  or,  more  accurately  speaking,  of  a  notochord,  a  back- 
bonelike structure.  Now,  an  insect  and  a  vertebrate  diverge  very 
soon  in  their  development  from  each  other;  but  two  insects,  such  as  a 
beetle  and  a  honeybee,  or  any  two  vertebrates,  such  as  a  frog  and  a 
pigeon,  do  not  diverge  from  each  other  so  soon.  That  is,  all  vertebrate 
animals  diverge  in  one  direction  from  the  other  great  groups,  but  all 
the  members  of  the  great  group  keep  together  for  some  time  longer. 
Then  the  subordinate  groups  of  the  Vertebrata,  such  as  the  fishes,  the 
birds,  and  the  others,  diverge,  and  still  later  the  different  kinds  of 
animals  in  each  of  these  groups  diverge  from  each  other. 

That  the  course  of  development  of  any  animal  from  its  beginning 
to  fully  developed  adult  form  is — in  all  its  essentials — fixed  and  certain 


EVIDENCES  FROM  EMBRYOLOGY  169 

is  readily  seen.  All  rabbits  develop  in  the  same  way;  every  grass- 
hopper goes  through  the  same  developmental  changes  from  single  egg 
cell  to  the  full-grown,  active  hopper  as  every  other  grasshopper  of  the 
same  kind — that  is,  development  takes  place  according  to  certain 
natural  laws;  the  laws  of  animal  development.  These  laws  may  be 
roughly  stated  as  follows:  All  many-celled  animals  begin  life  as  a 
single  cell,  the  fertilized  egg  cell;  each  animal  goes  through  a  certain 
orderly  series  of  developmental  changes  which,  accompanied  by  growth 
leads  the  animal  to  change  from  a  single  cell  to  the  many-celled,  com- 
plex form  characteristic  of  the  species  to  which  the  animal  belongs; 
this  development  is  from  simple  to  complex  structural  condition;  the 
development  is  the  same  for  all  individuals  of  one  species.  While  all 
animals  begin  development  similarly,  the  course  of  development  in 
the  different  groups  soon  diverges,  the  divergence  being  of  the  nature 
of  a  branching,  like  that  shown  in  the  growth  of  a  tree.  In  the  free 
tips  of  the  smallest  branches  we  have  represented  the  various  species 
of  animals  in  their  fully  developed  condition,  all  standing  more  or  less 
clearly  apart  from  each  other.  But  in  tracing  back  the  development 
of  any  kind  of  animal  we  soon  come  to  a  point  where  it  very  much 
resembles  or  becomes  apparently  identical  with  the  development  of 
some  other  kind  of  animal,  and,  in  addition,  the  stages  passed  through 
in  the  developmental  course  may  very  much  resemble  the  fully  devel- 
oped, mature  stages  of  lower  animals.  To  be  sure,  any  animal  at  any 
stage  in  its  existence  differs  absolutely  from  any  other  kind  of  animal, 
in  that  it  can  develop  into  only  its  own  kind  of  animal.  There  is  ^ 
something  inherent  in  each  developing  animal  that  gives  it  an  identity 
of  its  own.  Although  in  its  young  stages  it  may  be  hardly  distin- 
guishable from  some  other  kind  of  animal  in  similar  stages,  it  is  sure 
to  come  out,  when  fully  developed,  an  individual  of  the  same  kind  as 
its  parents  were  or  are.  A  very  young  fish  and  a  very  young  sala- 
mander are  almost  indistinguishably  alike,  but  one  is  sure  to  develop 
into  a  fish  and  the  other  into  a  salamander.  This  certainty  of  an 
embryo  to  become  an  individual  of  a  certain  kind  is  called  the  law  oV 
heredity.  Viewed  in  the  light  of  development,  there  must  be  as  great 
a  difference  between  one  egg  and  another  as  between  one  animal  and 
another,  for  the  greater  difference  is  included  in  the  less. 

The  significance  of  the  developmental  phenomena  is  a  matter  about 
which  naturalists  have  yet  very  much  to  learn.  It  is  believed,  how- 
ever, by  practically  all  naturalists  that  many  of  the  various  stages  in 
the  development  of  an  animal  correspond   to  or  repeat,  in   many 


I70     READINGS  IN  EVOLUTION,   GENETICS,  AND  EUGENICS 

fundamental  features  at  least,  the  structural  condition  of  the  animal's 
ancestors.     Naturalists   believe   that   all   backboned   or   vertebrate 


Fig.  36. — Stages  in  the  development  of  the  prawn,  Peneus  potimirlum.  A 
Nauplius  larva;  B,  first  zoea  stage;  C,  second  zoea  stage.  (From  Jordan  and 
Kellogg,  after  Fritz  M tiller.) 


Fig.  37. — Later  stages  in  the  development  of  the  prawn,  Peneus  potimiriiim. 
D,  Mysis  stage;  £,  adult  stage.     {From  Jordan  and  Kellogg.) 


EVIDENCES  FROM  EMBRYOLOGY 


171 


animals  are  related  to  each  other  through  being  descended  from  a 
common  ancestor,  the  first  or  oldest  backboned  animal.  In  fact,  it  is 
because  all  these  backboned  animals — the  fishes,  the  batrachians,  the 
reptiles,  the  birds,  and  the  mammals — have  descended  from  a  common 
ancestor  that  they  all  have  a  backbone.  It  is  believed  that  the 
descendants  of  the  first  backboned  animal  have  in  the  course  of  many 
generations  branched  off  little  by  little  from  the  original  type  until 
there  came  to  exist  very  real  and  obvious  differences  among  the  back- 
boned animals — differences  which  among  the  living  backboned  animals 
are  familiar  to  all  of  us.  The  course  of  development  of  an  individual 
animal  is  believed  to  be  a  very  rapid  and  evidently  much  condensed  and 
changed  recapitulation  of  the  history 
which  the  species  or  kind  of  animal  to 
which  the  developing  individual  belongs 
has  passed  through  in  the  course  of  its 
descent  through  a  long  series  of  gradually 
changing  ancestors.  If  this  is  true,  then 
we  can  readily  understand  why  a  fish 
and  a  salamander,  a  tortoise,  a  bird,  and 
a  rabbit,  are  all  much  alike,  as  they 
really  are,  in  their  earlier  stages  of 
development,  and  gradually  come  to 
differ  more  and  more  as  they  pass 
through  later  and  later  developmental 
stages.  A  crab  has  a  tail  in  one  of  its 
developmental  stages,  so  that  at  that 
time  it  looks  Hke  and  really  is  like  the  Fig.  38.— Metamorphosis  of  a 
mature  stage  of  some  tailed  crustacean    barnacle, Lc/>a5.   a, larva;  6, adult. 

i-i  r  ^         A  1  1         I'll!        (From  Jordan  and  Kellogg.) 

like  a  crayfish.    A  barnacle,  which  looks 

a  little  like  a  crayfish  or  crab  in  its  ma- 
ture stage,  is  hardly  to  be  distinguished  in  its  immature  life  from  a 
young  crab  or  lobster.  Sacculina,  which  is  a  still  more  degenerate 
crustacean,  is  only  a  sort  of  feeding  sac  with  rootlet-like  processes 
projecting  into  the  body  of  the  host  crab  on  which  it  lives  as  a 
parasite,  but  the  young  free-swimming  Sacculina  is  essentially  like  a 
barnacle,  crayfish,  or  crab  in  its  young  stage. 

However,  it  is  obvious  that  this  recapitulation  or  repetition  of 
ancestral  stages  is  never  perfect,  and  it  is  often  so  obscured  and  modi- 
fied by  interpolated  adaptive  stages  and  characters  that  but  little  of  an 
animal's  ancestry  can  be  learned  from  a  scrutiny  of  its  development. 


172      READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

The  fascinating  biogenetic  law  of  Miiller  and  Haeckel  summed  up 
in  the  phrase,  ^^ ontogeny  is  a  recapitulation  of  phytogeny, ^^  must  not 
be  too  heavily  leaned  on  as  a  support  for  any  speculations  as  to  the 
phyletic  affinities  of  any  species  or  group  of  species  of  organisms. 
''Embryology  is  an  ancient  manuscript  with  many  of  the  sheets  lost, 
others  displaced,  and  with  spurious  passages  interpolated  by  a  later 
hand." 


CHAPTER  XII 
CRITIQUE  OF  THE  RECAPITULATION  THEORY' 

W.    B.    SCOTT 

Embryology  is  the  study  of  the  development  of  the  individual 
organism  from  its  beginning  in  the  egg  to  the  attainment  of  the  adult 
condition.  This  individual  development  is  called  ontogeny  and  the 
question  of  the  relation  of  ontogeny  to  the  ancestral  history  of  the 
species,  or  phytogeny,  constitutes  one  of  the  main  problems  of  embr\^- 
ology.  Around  this  problem  many  controversies  have  raged,  contro- 
versies which  have  by  no  means  arrived  at  a  definite  solution,  even 
to-day.  Thirty  years  ago  the  "recapitulation  theory"  was  well-nigh 
universally  accepted,  according  to  which  the  individual  development, 
or  ontogeny,  was  regarded  as  an  abbreviated  repetition  of  the  ances- 
tral history  of  the  species,  or  phylogeny.  Haeckel  called  this  theory 
the  "fundamental  biogenetic  law"  and  upon  it  he  established  his 
whole  "History  of  Creation."  Nowadays,  that  "fundamental  law" 
is  very  seriously  questioned  and  by  some  high  authorities  is  altogether 
denied.  However,  even  those  who  take  this  extreme  position  con- 
cerning the  recapitulation  theory  see  in  the  facts  of  embryology  one 
of  the  strongest  supports  of  the  doctrine  of  evolution. 

It  was  very  early  recognized  that  the  recapitulation  theory  could 
not  be  applied  with  literal  exactness,  but  was  subject  to  certain 
important  exceptions  and  qualifications. 

I.  That  the  history  must  have  been  enormously  abbreviated. 
After  three  weeks  of  incubation  the  tiny  speck  of  protoplasm,  which 
forms  a  circular  mark  on  the  yolk  of  a  hen's  egg,  is  developed  into  a 
fully  formed  chick,  ready  for  hatching  and  able  in  large  degree  to  take 
care  of  itself.  On  the  other  hand,  the  evolution  of  birds  from  their 
invertebrate  ancestors,  through  the  fishes,  amphibians,  and  reptiles, 
the  separation  of  the  gallinaceous  stock  from  other  birds  and  the 
differentiation  of  this  particular  species  were  extremely  slow  processes, 
extending  through  unnumbered  millions  of  years.  Admitting  reca- 
pitulation to  the  fullest  extent,  it  is  evidently  a  physical  impossibility 

^  From  W.  B.  Scott,  The  Theory  of  Evolution  (copyright  191 7).  Used  by- 
special  permission  of  the  publishers,  The  Macmillan  Company, 

173 


174     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

that  it  should  be  a  perfect  repetition  of  phylogeny;  very  much  of  the 
long  story  must  of  necessity  be  omitted. 

2.  Through  all  the  stages  of  development  the  embryo  must  be 
rendered  able  to  live  and  grow  and  thrive  through  adaptation  to  its 
surroundings  and  changes  in  its  environment.  In  some  animals 
development  takes  place  within  the  body  of  the  mother;  in  others  the 
embryo  is  protected  by  the  hard  egg-shell,  as  in  birds,  while  the  eggs 
of  certain  fishes  and  many  invertebrates  float  freely  in  the  sea  and  are 
almost  without  protection.  Such  differences  in  environment  necessi- 
tate differences  in  the  mode  of  development,  while  the  presence  or 
absence  of  a  large  amount  of  inert  food-material,  or  yolk,  exerts  a  great 
influence  in  determining  the  steps  of  ontogeny. 

3.  Many  animals  pass  through  a  larval  stage  of  development,  in 
which  the  immature  young  leads  an  independent  and  self-sustaining 
existence,  during  which  it  is  very  different  in  appearance  and  structure 
from  its  adult  parents.  Familiar  instances  of  this  mode  of  develop- 
ment are  to  be  found  in  the  tadpole,  which  is  the  larva  of  the  frog,  and 
the  caterpillar,  the  larva  of  a  butterfly.  Larvae  are  fully  subject  to 
the  struggle  for  existence  and  must  adapt  themselves  to  their  environ- 
ment and  to  changes  in  that  environment,  exactly  as  do  adults,  if  they 
are  to  survive.  In  this  way  many  changes  are  introduced  into  the 
ontogeny  which  can  have  no  phylogenetic  significance.  It  is  found  in 
several  known  instances,  that  nearly  allied  species,  living  under 
different  conditions,  have  quite  different  modes  of  ontogeny,  though 
their  ancestral  history  must  have  been  substantially  identical.  In  one 
and  the  same  species  of  marine  worms,  for  example,  which  inhabits 
both  the  warm  Mediterranean  and  the  cold  waters  of  the  North  Sea, 
the  larva  of  the  northern  form  is  quite  distinct  from  that  of  the 
southern.  In  attempting  to  interpret  the  meaning  of  embryological 
facts,  it  is  thus  necessary  to  distinguish  sharply  between  those  features 
which  are  derived  from  a  long  inheritance,  and  are  therefore  called 
palingenetic,  from  those  which  have  been  secondarily  introduced  in 
response  to  the  changing  needs  of  embryonic  or  larval  life.  These 
secondary  features  are  termed  cenogenetic. 

''If  we  are  compelled  to  admit  that  cenogenetic  characters  are 
intermingled  with  palingenetic,  then  we  cannot  regard  ontogeny  as  a 
pure  source  of  evidence  regarding  phyletic  relationships.  Ontogeny 
accordingly  becomes  a  field  in  which  an  active  imagination  has  full 
scope  for  its  dangerous  play,  but  in  which  positive  results  are  by  no 
means  everywhere  to  be  obtained.     To  attain  such  results,  the  palin- 


THE  RECAPITULATION  THEORY  175 

genetic  and  cenogenetic  phenomena  must  be  sifted  apart,  an  operation 
which  required  more  than  one  critical  grain  of  salt.  On  what  grounds 
shall  this  critique  be  based  ?  Assuredly  not  by  way  of  a  vicious  circle 
on  the  ontogeny  again;  for  if  cenogenetic  characters  are  present  in  one 
case,  who  will  guarantee  that  a  second  case,  used  for  a  comparison  with 
the  first,  does  not  Hkewise  appear  in  cenogenetic  disguise  ?  If  it  once 
be  admitted  that  not  everything  in  development  is  palingenetic,  that 
not  every  ontogenetic  fact  can  be  accepted  at  its  face  value,  so  to 
speak,  it  follows  that  nothing  in  ontogeny  is  immediately  available 
for  the  critique  of  embryonic  development.  .The  necessary  critique 
must  be  drawn  from  another  source." 

These  remarks  of  Gegenbaur's  were  called  forth  by  the  state  of 
wild  speculation  into  which  embryological  work  had  fallen.  As  there 
were  no  generally  accepted  canons  of  interpretation  for  the  facts  of 
embryological  development,  different  writers  interpreted  these  facts 
in  the  most  divergent  and  contradictory  manner,  resulting  in  a  chaotic 
confusion,  which  led  to  a  strong  reaction  against  the  whole  method, 
though  there  can  be  little  doubt  that  this  reaction  has  gone  too  far. 

"It  must  be  evident  to  any  candid  observer,  not  only  that  the 
embryological  method  is  open  to  criticism,  but  that  the  whole  fabric 
of  morphology,  so  far  as  it  rests  upon  embryological  evidence,  stands 
in  urgent  need  of  reconstruction.  For  twenty  years  embryological 
research  has  been  largely  dominated  by  the  recapitulation  theory; 
and  unquestionably  this  theory  has  illuminated  many  dark  places  and 
has  solved  many  a  perplexing  problem  that  without  its  aid  might  have 
remained  a  standing  riddle  to  the  pure  anatomist.  But  while  fully 
recognizing  the  real  and  substantial  fruits  of  that  theory,  we  should  not 
close  our  eyes  to  the  undeniable  fact  that  it,  like  many  another  fruit- 
ful theory,  has  been  pushed  beyond  its  legitimate  limits.  It  is  largely 
to  an  overweening  confidence  in  the  validity  of  the  embryological 
evidence  that  we  owe  the  vast  number  of  the  elaborate  hypothetical 
phylogenies  which  confront  the  modern  student  in  such  bewildering 
confusion.  The  inquiries  of  such  a  student  regarding  the  origin  of  any 
of  the  great  principal  types  of  animals  involve  him  in  a  labyrinth  of 
speculation  and  hypothesis  in  which  he  seeks  in  vain  for  conclusions 
of  even  an  approximate  certainty." 

Many  other  equally  vigorous  and  well-deserved  criticisms  of  the 
embryological  method  might  be  cited,  but  it  should  be  emphasized  that 
these  criticisms  are  all  directed  against  the  application  of  the  method 
to  the  solution  of  definite  and  concrete  problems  of  descent  and 


176     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

relationship.'  None  of  them  denies  and  many  strongly  affirm  that 
embryology  affords  some  of  the  strongest  and  most  convincing  evi- 
dence in  favor  of  the  evolutionary  theory. 

Let  us  examine  some  of  this  evidence.  To  begin  with,  it  should 
be  noted  that,  in  following  out  the  ontogeny  or  individual  develop- 
ment, the  observer  witnesses  the  formation  of  something  new,  not 
merely  the  enlargement  and  unfolding  of  a  pre-existing  organism, 
though  the  theory  of  preformation,  which  was  widely  accepted  in  the 
eighteenth  century,  looked  upon  ontogeny  precisely  in  that  way,  as 
the  growth  of  a  germ  which  was  the  miniature  of  the  parent.  Such  a 
theory  was  possible  only  before  the  development  of  microscopic 
technique  had  enabled  the  observer  to  detect  the  actual  successive 
steps  of  change.  The  egg  is  a  single  cell,  with  the  nucleus  and  all  the 
parts  of  other  undifferentiated  cells,  though  it  may  be  enormously 
enlarged  by  the  presence  of  food- yolk.  In  the  hen's  egg  this  food-yolk 
is  quite  inert  and  the  activity  of  development  is  confined  to  the  minute 
disc  of  protoplasm  on  the  outside  of  the  yolk,  while  in  the  frog's  egg 
the  yolk  is  disseminated,  though  not  uniformly,  throughout  the  egg 
and  in  the  mammaUan  egg,  which  is  microscopic  in  size,  there  is  no 
yolk.  It  is  a  very  remarkable  fact  that  all  of  the  vertebrated  animals, 
fishes,  amphibians,  reptiles,  birds  and  mammals,  however  different 
their  habits  and  modes  of  life,  have  a  mode  of  ontogeny  which  is  of 
even  more  characteristically  and  unmistakably  the  same  plan  than  is 
the  type  of  their  adult  structure,  which  was  described  in  the  last 
chapter.  The  egg,  or  the  active  portion  of  it,  divides  in  a  definite  and 
regular  manner  into  a  very  large  number  of  cells,  which  arrange  them- 
selves in  definite  layers,  an  outer  and  an  inner,  and  within  these  layers 
cell-aggregates  form  incipient  organs,  which,  step  by  step,  take  on  the 
adult  condition.  Not  only  is  the  plan  and  type  of  development 
essentially  similar  throughout  the  whole  phylum  of  the  vertebrates, 
but,  in  accordance  with  the  recapitulation  theory,  many  structural 
features  which  are  permanent  in  lower  forms  appear  in  the  embryos  of 
higher  and  more  advanced  types.  In  the  latter,  however,  these 
features  are  transitory  and,  in  the  course  of  development,  they  either 
disappear,  or  are  so  modified  as  to  be  very  different,  sometimes  unrecog- 
nizable, in  the  adults. 

At  a  certain  stage  of  the  ontogeny  the  embryo  of  a  mammal  has 
gill-pouches  like  a  fish,  the  skeletal  supports  of  the  gill-pouches,  the 
arteries  and  veins  which  supply  them  with  blood,  the  structure  of  the 
heart,  in  short,  the  entire  plan  of  the  circulatory  system  is  fish-like. 


THE  RECAPITULATION  THEORY 


177 


At  a  later  stage  most  of  the  gill-pouches  have  been  obliterated,  but  one 
is  retained  and  converted  into  the  Eustachian  canal,  which  connects 
the  throat  with  the  middle  ear,  inside  of  the  ear-drum.  Similarly,  the 
embryological  evidence  shows  that  the  lungs  of  air-breathers  have  been 
derived  from  the  swim-bladder  of  fishes,  a  conclusion  which  had 
already  been  reached  by  comparative  anatomy,  for  in  a  remarkable 


A  B  ^ 

Fig.   39. — Embryos  in  corresponding  stage  of  development  of  shark  (A), 
fowl  (B),  and  man  (C);  g,  gill  slits.     {From  Scott.) 


group,  known  as  the  Dipnoi  or  lung-fishes,  the  air-bladder  is  utilized 
for  purposes  of  respiration. 

It  has  been  objected  that,  while  embryology  may  prove  relation- 
ship within  a  single  type,  it  fails  to  demonstrate  any  connection 
between  different  types,  but  this  is  not  altogether  true.  The  Tuni- 
cata,  a  curious  group  of  marine  animals  once  referred  to  the  Mollusca, 
are  shown  by  their  ontogeny  to  be  related  to  the  vertebrates  and  the 
same  is  true  of  certain  marine  worms  {Balanoglossus).  Indeed,  most 
modern  zoologists  have  adopted  a  scheme  of  classification,  in  which 


1 78      READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGI:NICS 

the  type  Chordata  includes  not  only  the  true  vertebrates,  but  also  the 
Lancelet  {Amphioxiis) ,  the  tunicates,  and  Bala  no  gloss  us;  this  scheme 
is  founded  upon  the  embryological  evidence.  Among  the  inverte- 
brates even  more  remarkable  examples  have  been  observed.  Such 
radically  different  types  as  the  segmented  worms  and  the  shell- 
fish (Mollusca)  are  brought  into  relationship  by  their  ontogeny  and 
their  closely  similar  types  of  larvae,  as  are  also,  though  less  distinctly, 
the  brachiopods  or  lamp-shells,  and  the  Bryozoa.  The  Horseshoe- 
crab,  or  King-crab,  so  abundant  along  our  Atlantic  coast,  was  long 
of  uncertain  affinities;  originally  referred  to  the  Crustacea,  largely 
because  of  its  marine  habits  of  life,  embryology  makes  much  more 
probable  its  relationship  to  the  air-breathing  scorpions  and  spiders,  a 
result  which  has  been  examined  previously  from  another  point  of  view 
in  connection  with  blood-tests. 

Even  before  the  publication  of  Darwin's  Origin  of  Species  one 
of  the  great  stumbling  blocks  in  the  way  of  the  theory  of  special  crea- 
tion was  the  existence  in  a  great  many  animals  of  rudimentary  organs, 
or  such  as  are  so  far  reduced  and  atrophied  as  to  be  of  no  service  to 
their  possessors.  An  analogy  employed  by  my  lamented  friend, 
Mr.  Richard  Lydekker,  may  be  advantageously  repeated  here.  Let  us 
suppose  that  a  screw-steamer,  with  longitudinal  shaft  leading  aft  from 
the  engine-room  to  the  stern,  where  it  carries  the  propeller,  should,  on 
close  examination,  reveal  many  signs  that  it  has  originally  been  a 
''side- wheeler,"  or  paddle-boat.  Recognizable  remnants  of  paddle- 
boxes,  of  bearings  for  a  transverse  shaft,  and  the  like,  are  found;  what 
would  be  the  inevitable  conclusion  ?  No  one  would  maintain  that  a 
naval  architect,  in  possession  of  his  senses,  in  constructing  a  screw- 
steamer  would  deliberately  introduce  features  which  are  useful  and 
appropriate  only  in  a  paddle-boat.  The  only  reasonable  explanation 
would  be  that  the  vessel  had  originally  been  built  as  a  paddle-boat  and 
had  subsequently  been  converted  into  a  screw-steamer  and  in  the 
conversion  it  had  not  been  found  necessary  completely  to  eradicate  all 
traces  of  the  original  construction.  Obviously,  the  same  reasoning 
applies  to  rudimentary  organs.  The  only  satisfactory  explanation  of 
such  useless  remnants  is  that  their  possessors  are  descendants  of 
ancestors  in  which  those  organs  were  fully  functional.  It  seems  quite 
absurd  to  assume  that,  in  a  separately  and  specially  created  animal, 
useless  structures,  reminiscent  of  other  animals  in  which  the  same 
structures  are  useful  and  valuable,  should  be  included,  merely  to 
indicate  ideal  relationships  and  community  of  plan. 


THE  RECAPITULATION  THEORY  179 

It  was  sought  to  break  the  force  of  this  very  serious  objection  to 
the  theory  of  special  creation  by  saying  that  apparently  useless  organs 
may  nevertheless  have  functions  which  are  still  unknown  to  us  and 
may  be  revealed  by  future  discovery.  In  certain  cases,  like  that  of  the 
thyroid  gland  in  the  neck,  this  contention  has  been  justified,  but  there 
are  many  others  to  which  it  does  not  apply.  For  example,  in  the  great 
and  varied  whale-tribe  (order  Cetacea)  which  includes  the  right,  or 
whalebone,  whales,  the  sperm-whales,  the  porpoises,  dolphins,  etc., 
the  forelimbs  have  been  converted  into  swimming  paddles,  but  the 
hind  limbs  appear  to  have  vanished  completely,  leaving  no  externally 
visible  trace.  Internally,  however,  recognizable  remnants  of  the  hind 
limb-bones  may  be  found  in  various  stages  of  reduction,  which  differ 
in  the  different  members  of  the  order.  In  the  Greenland  Right  Whale 
the  hip-bone,  thigh-bone  and  shin-bone  are  indicated;  in  the  Fin  whale 
only  the  hip-bones  and  a  minute  rudiment  of  the  thigh-bone  are  to  be 
found;  in  the  toothed  whales  only  an  almost  unrecognizable  remnant 
of  the  hip-bone  is  left  and  in  one  of  the  dolphins  even  that  has  dis- 
appeared. Similarly,  the  snakes  have  lost  their  limbs  completely,  so 
far  as  external  appearance  is  concerned,  and  in  most  members  of  the 
group  no  trace  of  Hmbs  is  to  be  found  on  dissection,  but  in  certain 
snakes  the  rudiments  of  limbs  are  to  be  detected.  Leaving  aside  all 
preconceptions,  which  is  the  more  probable  explanation  of  such 
phenomena,  the  theory  of  special  creation  or  the  theory  of  evolution  ? 

Even  if  it  were  admitted  that  all  rudimentary  organs  and  struc- 
tures found  in  the  adult  have  a  certain  unknown  use  and  value,  no  one 
could  maintain  this  with  regard  to  the  countless  instances  of  structures 
which  are  developed  in  the  embryo,  but  disappear  entirely  before 
birth.  It  is  possible  to  mention  but  a  very  few  of  such  instances  out 
of  the  great  number  that  have  already  been  observed  and  recorded, 
but  these  few  will  sufifice  to  illustrate  the  principle  involved. 

"Examples  of  this  may  be  cited  from  the  most  widely  different 
groups:  in  the  embryo  of  insects,  especially  of  beetles,  pairs  of  legs 
are  formed  within  the  egg,  not  only  on  the  head  and  thorax,  but  also 
on  the  abdomen,  but  while  those  on  the  head  are  transformed  into 
mouth-parts,  those  on  the  thorax  are  farther  developed  in  their  joint- 
ing and  musculature  to  be  locomotive  legs,  those  on  the  abdomen  are 
again  resorbed.  In  many  fresh-water,  worms,  the  eggs  of  which  are 
laid  in  a  cocoon,  from  which  they  are  hatched  as  a  finished,  minute, 
crawling  worm,  larval  organs  are  nevertheless  formed,  which  recall 
those  of  the  Trochophore,the  larva  of  the  original  worms,  which  swims 


i8o      READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

■freely  in  the  sea.  However,  these  larval  organs  ....  are  never 
properly  functional,  since  no  actually  free-swimming  larva  is  developed 
but  the  embryo  merely  floats  in  the  albuminous  fluid  of  the  cocoon. 

'^  A  particularly  beautiful  example  is  offered  by  the  whales  in  their 
embryological  development,  which  has  been  thoroughly  studied  by 
Kukenthal.  In  the  adult  condition  they  show  only  the  anterior 
extremities,  but  in  the  embryo  the  posterior  pair,  with  their  skeletal 
parts,  are  formed,but  are  afterwards  completely  atrophied.  Although 
they  are  mammals,  in  the  adult  condition  they  have  absolutely  no 
covering  of  hair,  since  in  their  aquatic  life  another  and  more  effective 
protection  against  loss  of  heat  is  given  by  means  of  a  thick  layer  of 
blubber;  only  a  few  coarse  bristles,  partly  with  particular  functions, 
have  persisted  on  a  few  parts  of  the  body.  But  in  the  embryo  a  dense 
covering  of  hair  is  formed,  which  is  later  transformed  in  a  peculiar 
manner  and  atrophied.  Further,  a  series  of  whales  have  no  teeth  in 
the  adult  condition,  but  only  the  well-known,  eel-trap-like,  horiiy 
plates,  from  which  whale-bone  is  produced.  Nevertheless,  in  the 
embryo  there  is  a  dentition  of  numerous  teeth,  which  are,  however, 
resorbed,  without  ever  piercing  the  gum."^ 

Throughout  the  great  group  of  the  ruminants,  which  includes  the 
oxen,  buffaloes,  bison,  sheep,  goats,  antelopes,  deer  and  giraffes,  the 
collar-bone  is  invariably  lacking,  since  it  is  superfluous  on  account  of 
the  exclusively  locomotive  manner  in  which  the  fore  legs  are  employed. 
In  the  embryo  sheep  the  collar-bone  is  established  and  even,  to  some 
extent  ossified,  but  is  subsequently  resorbed  and  disappears  entirely. 
No  doubt,  the  collar-bone  will  be  found  in  many  other  embryo  rumi- 
nants, when  the  proper  examination  shall  have  been  made,  but  its 
demonstrated  presence  in  the  foetal  sheep  is  sufficiently  striking.  In 
the  higher  mammals  the  number  of  teeth  was  originally  44,  or  11  on 
each  side  of  both  upper  and  lower  jaws,  but  in  most  of  the  modern  or 
existing  groups  of  these  higher  mammals  this  number  has  been  very 
considerably  reduced  through  the  suppression  of  certain  teeth.  We 
have  every  reason  to  believe  that  the  ancestors  of  the  forms  with 
reduced  dentition  possessed  teeth  in  full  numbers  and  that  there  has 
actually  been  a  loss  of  teeth  in  the  course  of  descent.  This  conclusion 
is  abundantly  confirmed  by  the  facts  of  embry.ology.  Take,  for 
example,  the  great  group  of  the  gnawing  mammals  or  Rodentia,  in 
which  the  front  teeth  or  incisors,  above  and  below,  are  reduced  to  one 
on  each  side,  except  in  the  rabbits.     The  incisors  are  chisel-shaped  and 

^  Otto  Maas,  Die  Ahstammungslchrc,  pp.  273-74. 


THE  RECAPITULATION  THEORY  i8i 

are  faced  with  hard  enamel,  so  that  the  action  of  the  upper  teeth  upon " 
the  lower  keeps  the  cutting  edges  extremely  sharp;  these  teeth  do  not 
form  roots,  but  continue  to  grow  throughout  the  lifetime  of  the  animal. 
Between  the  chisel-like  incisors  and  the  grinding  teeth,  there  is  a  long 
toothless  gap,  which,  we  assume,  was,  in  the  ancestors  of  the  rodents, 
occupied  by  the  second  and  third  incisors,  the  canine  and  two  or  more 
grinders.  This  conclusion  is  justified  by  the  facts  of  embryology; 
for  instance,  in  the  embryo  of  the  squirrel  several  of  the  missing  teeth 
are  begun  as  distinct  tooth-germs,  but  fail  to  develop,  never  cut  the 
gum  and  are  resorbed  before  birth. 

All  available  evidence  points  to  the  conclusion  that  birds  are 
descended  from  reptiles,  a  conclusion  which  is  especially  strengthened 
by  the  facts  of  palaeontology  and  will  be  examined  more  at  length 
in  the  following  lecture.  Such  a  descent  explains  many  otherwise 
puzzling  features  in  the  ontogeny  of  birds,  in  which  reptilian  charac- 
teristics appear  in  transitory  fashion  and  are  either  modified  so  as  to 
take  on  typically  bird-like  character,  or  are  suppressed  altogether.  A 
remarkable  example  of  this  is  the  formation  of  rudimentary  teeth  in 
certain  embryonic  birds,  followed  by  their  resorption  and  disappear- 
ance before  hatching. 

It  can  hardly  be  contended  that  these  rudimentary  structures, 
which  are  confined  to  the  embryonic  stages  of  development  and  of 
which  no  trace  remains  in  the  adult,  are  so  indispensable  to  the 
processes  of  ontogeny,  that  they  were  specially  created  to  serve  this 
temporary  purpose.  For  such  a  contention  there  is  not  a  particle 
of  evidence  and  the  theory  of  evolution,  which  regards  these  structures 
as  useless  remnants,  due  to  inheritance  from  ancestors  in  which  the 
structures  are  functional,  offers  much  the  most  satisfactory  solution 
of  the  problem  that  has  yet  been  suggested. 

Embryology  further  shows  that  evolution  is  not  invariably  an 
advance  from  lower  and  simpler  to  higher  and  more  complex  t>pes, 
but  may  be  by  way  of  degeneration  and  degradation.  The  adoption 
of  a  parasitic  mode  of  life  is  very  apt  to  cause  such  degradation,  and 
some  very  remarkable  instances  of  the  degene  ration  of  parasites  have 
been  observed.  An  instructive  example  that  may  be  cited  is  that  of 
Sacculina,  a  nondescript  creature  that  is  parasitic  on  certain  species 
of  crabs.  The  parasite  is  attached  to  the  body  of  its  victim,  under- 
neath the  tail,  by  means  of  root-hke  fibre  s  which  penetrate  and  ramif\' 
throughout  the  interior  of  the  crab.  The  root-like  fibres  absorb  nutri- 
ment and  convey  it  to  the  body  of  the  parasite,  which  is  reduced  to  a 


1 82      READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

mere  bag,  without  appendages,  muscles,  nervous  system,  sensory- 
apparatus,  digestive  tract,  or  any  determinable  organs  save  those  of 
reproduction.  The  creature  has  the  power  of  assimilating  the  nutri- 
tive juices  which  are  conveyed  to  it  by  the  root-like  filaments  from  the 
body  of  its  host,  and  the  power  of  reproduction,  and  it  must  have  some 
respiratory  and  excretory  capacity,  though  there  are  neither  gills  nor 
glands.  From  an  examination  of  the  adult  parasite  alone,  it  would  be 
quite  impossible  to  classify  it  and  determine  the  type  and  class  to 
which  it  should  be  referred,  but  embryology  solves  the  problem.  From 
the  egg  is  hatched  a  free-swimming  larva,  which  has  jointed  append- 
ages, nervous,  muscular  and  digestive  systems  and,  in  short,  clearly 
belongs  to  that  group  of  the  Crustacea  which  includes  the  barnacles. 
This  is  degeneration  carried  nearly  to  the  utmost  possible  extreme  and 
yet  the  individual  development  shows  the  derivation  of  this  otherwise 
problematical  parasite  and  the  steps  through  which  it  passed  in  its 
deterioration. 

It  was  stated  above  that  several  distinguished  naturalists  alto- 
gether reject  the  recapitulation  theory  as  a  means  of  interpreting  the 
facts  of  embryology.  They  do  this  on  the  ground  that,  inasmuch  as 
changes  and  innovations  in  form  or  structure  must  arise  in  the  germ- 
plasm,  at  the  very  beginning  of  ontogeny,  there  is  no  reason  why  such 
changes  might  not  involve  the  whole  course  of  embryological  develop- 
ment. To  my  mind  this  a  priori  objection  to  the  recapitulation  theory 
is  quite  without  force  in  view  of  the  great  body  of  observed  facts,  but 
there  is  no  time  to  enter  upon  a  discussion  of  such  an  abstract  and 
difficult  problem.  For  our  present  purpose,  however,  it  is  important 
to  note  that  these  objectors  are  staunch  evolutionists  and  find  in  the 
community  of  mode  in  ontogeny  between  different  classes  of  organ- 
isms one  of  the  strongest  arguments  in  support  of  the  evolutionary 
doctrine. 


PART  III 
THE  CAUSAL  FACTORS  OF  ORGANIC  EVOLUTION 


CHAPTER  XIII 

INTRODUCTORY  STATEMENT 
H.  H.  Newman 

Any  investigation  of  the  causes  of  evolution  must  be  preceded  by  a 
survey  of  the  facts  to  be  explained.  Some  of  the  principal  facts 
which  must  be  taken  into  account  have  already  been  placed  before  the 
reader  in  the  preceding  section  dealing  with  evidences  of  evolution. 
If  there  were  no  other  good  reason  for  dealing  with  those  materials 
before  beginning  a  discussion  of  causal  theories  of  evolution,  the  peda- 
gogical reason  would  be  sufficient,  because,  until  there  is  something 
to  explain,  the  necessity  for  an  explanation  does  not  arise.  We  are  of 
course  aware  that  some  writers  prefer  to  deal  with  the  facts  of  palaeon- 
tology, geographic  distribution,  classification,  comparative  anatomy 
embryology,  etc.,  after  a  discussion  of  the  causes  of  evolution.  Their 
avowed  reason  for  this  order  of  treatment  is  that  the  net  results  of  a 
discussion  of  the  causes  underlying  evolution  may  be  used  as  a  means 
of  more  fully  analyzing  the  facts.  This  is  indeed  true,  but  it  is  also 
true  that  facts  should  come  first  and  explanations  afterward.  As  a 
final  step,  the  facts  profitably  may  be  re-examined  in  the  light  of  causal 
hypotheses. 

One  of  the  outstanding  facts  of  animate  nature  is  the  phenomenon 
of  adaptation.  No  naturalist  has  failed  to  note  and  marvel  at  the 
adaptiveness  or  fitness  of  organisms  to  their  environment  and  that  of 
parts  of  organisms  for  particular  functions  or  activities.  One  of  the 
most  difficult  problems  in  evolution  is  the  problem  of  the  origin  and  the 
perfection  of  adaptations,  and  most  causal  theories  of  evolution  have 
been  aimed  largely  at  an  explanation  of  adaptation.  Consequently, 
before  we  enter  upon  a  formal  discussion  of  the  causal  theories  we  shall 
introduce  an  outline  of  some  of  the  main  facts  about  adaptations. 

By  way  of  introduction  it  should  also  be  pointed  out  that  the 
causes  of  evolution  are  not  all  of  equal  value.  Some  of  the  causes  are 
to  be  conceived  of  as  primary,  others  as  secondary,  or  even  tertiary. 
Variation,  for  example,  is  absolutely  primary  in  importance.  Without 
variation,  change,  which  is  the  very  essence  of  evolution,  would  of 
course  be  impossible.  Not  less  important  is  heredity;  for  unless  there 
be  some  factor  which  fixes  variation  so  that  it  becomes  a  racial  asset, 

185 


1 86      READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

there  can  be  no  real  racial  progress;  and  evolution  is  nothing  more  or 
less  than  racial,  as  opposed  to  individual,  progress.  So  obvious  did 
this  seem  that  Charles  Darwin  accepted  as  axiomatic  the  general  facts 
of  variation  and  heredity  and  proceeded  at  once  to  a  discussion 
of  the  directive  factors  of  evolution.  Since  variation  and  heredity 
are  now  universally  conceded  to  be  primary  factors,  and  selection, 
the  Lamarckian  factor,  isolation,  orthogenesis,  etc.,  as  secondary 
or  guiding  factors,  it  would  seem  more  natural  to  proceed  first  to 
a  discussion  of  variation  and  heredity.  So  much  of  our  present 
knowledge  of  variation  and  heredity,  however,  is  dependent  upon  the 
background  furnished  by  Darwin  that  it  seems  to  us  a  more  effective 
pedagogical  order  to  consider  that  vast  and  intricate  conception  of 
evolution  which  was  first  given  life  and  unity  by  Charles  Darwin, 
and  has  come  now  to  be  known  as  '^ Darwinism." 

Just  how  broad  the  scope  of  Darwin's  work  and  how  important  a 
role  he  played  in  the  development  of  evolutionary  biology  is  indicated 
in  the  following  appreciation  of  Darwin  which  we  have  summarized 
largely  from  the  admirable  statement  in  Professor  J.  Arthur  Thom- 
son's book  Darwinism  and  Human  Life. 

WHAT   WE    OWE   TO    DARWIN 

1.  The  web  of  life — the  idea  of  linkages,  interdependencies,  cor- 
relations in  the  living  world.  The  idea  is  essentially  ecological  and  has 
been  expressed  elsewhere  as  "organic  equilibrium." 

2.  The  struggle  for  existence — the  inevitable  consequence  of  Mal- 
thus'  idea  of  overproduction.  This  struggle  is  both  inter-  and  intra- 
specific,  or  may  be  a  mere  struggle  against  fate  or  against  hard  condi- 
tions of  inorganic  environment. 

3.  Variability  of  living  creatures — an  idea  derived  from  the  study  of 
changes  under  domestication  and  of  diversity  among  wild  individuals 
belonging  to  the  same  species. 

4.  Natural  selection — the  central  idea  which  is  to  be  studied  pres- 
ently. 

5.  Vindication  of  the  evolution  idea. — Darwin  was  the  first  effec- 
tively to  marshal  the  evidences  of  evolution  in  sufficient  force  to  com- 
pel the  acceptance  of  the  fact  of  evolution.  Much  that  has  already 
been  presented  under  the  head  of  "Evidences  of  Evolution"  belongs 
to  Darwin.  The  placing  of  the  fact  of  evolution  on  a  sure  foundation 
is  believed  by  many  to  have  been  Darwin's  principal  contribution  to 
science. 


INTRODUCTORY  STATEMENT  187 

6.  The  descent  arid  ascent  of  Man — ''  a  recognition  of  man's  solidar- 
ity with  the  rest  of  creation,  of  his  afhUation  to  a  Simian  stock — that 
man  and  anthropoid  apes  are  collateral  branches  from  a  common  Pri- 
mate stock  which  remains  hidden  in  obscurity." 

7.  Liberation  of  intelligence. — ''The  Origin  of  Species  has  proved 
a  veritable  Magna  Charta  of  intellectual  liberties,  for,  as  no  other 
single  document  before  or  since,  it  has  released  the  thoughts  of  man 
from  the  trammels  of  unreasoned  conservatism  and  dogmatism." — 
H.  E.  Crampton. 

8.  Ideal  of  scientific  mood  and  method. — As  Professor  T.  H.  Morgan 
says,  "  It  is  the  spirit  of  Darwinism,  not  its  formulae,  that  we  proclaim 
as  our  best  heritage."  Darwin  was  the  first  great  evolutionist  to  use 
the  inductive  method,  that  of  first  securing  an  abundance  of  facts  and 
then  formulating  theories  to  explain  the  facts. 

The  above-stated  eight  points  give  us  an  idea  of  the  broader  con- 
cept of  Darwinism.  Today  the  term  "Darwinism"  has  come  to 
acquire  a  much  restricted  and  a  technical  meaning.  To  the  modern 
evolutionist  Darwinism  has  come  to  be  practically  synonymous  with 
"natural  selection,"  or  at  least  with  the  general  principle  of  "selec- 
tion," some  phases  of  which  are  termed  "neo-Darwinism."  Before 
we  can  adequately  enter  upon  a  study  of  Darwin's  most  characteristic 
causal  theory  of  evolution — the  natural-selection  theory — it  is  almost 
imperative  for  us  to  know  something  of  the  background  out  of  which 
this  conception  arose.  Already  we  have  presented  in  our  survey  of  the 
evidences  of  evolution  an  array  of  facts  most  of  which  were  known  to 
Darwin  and  in  accord  with  which  he  developed  his  causal  theories. 
But  we  cannot  afford  to  overlook  the  now  well-known  fact  that  what 
Darwinism  chiefly  aims  to  explain  are  the  phenomena  of  adaptation 
and  the  web  of  life.  These  phenomena  are  to  be  conceived  of  as  the 
background  of  Darwinism  and  will  be  dealt  with  as  such  in  the  next 
chapters. 


CHAPTER  XIV 

THE  BACKGROUND  OF  DARWINISM 

ADAPTATIONS 

H.  H.  Newman 

"The  adaptation  of  every  species  of  animal  and  plant  to  its 
en\'ironment,"  says  Jordan  and  Kellogg/  "is  a  matter  of  everyday 
observation.  So  perfect  is  this  adaptation  in  its  details  that  its  main 
facts  tend  to  escape  our  notice.  The  animal  is  fitted  to  the  air  it 
breathes,  the  water  it  drinks,  the  food  it  finds',  the  climate  it  endures, 
the  region  which  it  inhabits.  All  its  organs  are  fitted  to  its  functions: 
all  its  functions  to  its  environment.  Organs  and  functions  are  alike 
spoken  of  in  a  half-figurative  way  as  concessions  to  environment.  And 
all  structures  and  powers  are  in  this  sense  concessions,  in  another 
sense,  adaptations.  As  the  loaf  is  fitted  to  the  pan,  or  the  river  to  its 
bed,  so  is  each  species  fitted  to  its  surroundings.  If  it  were  not  so 
fitted,  it  would  not  live.  But  such  fitness  on  the  vital  side  leaves  large 
room  for  variety  in  characters  not  essential  to  the  life  of  the  animal. " 

The  authors  quoted  above  appreciate  what  is  perhaps  the  most 
significant  fact  about  adaptations:  that  the  adaptations  are  to  a  large 
extent  molded  by  the  environment  and  therefore  fit  the  environment. 
So  long  as  the  environment  remains  uniform,  a  given  species  will 
remain  unchanged,  except  for  minor  fluctuations  and  occasional 
mutations;  but  if  the  environment  changes,  sometimes  even  slightly, 
the  development  of  the  individual  responds  in  such  a  way  as  to  give  a 
radically  different  end  product.  So  we  may  conclude  that  a  large  part 
of  the  fitness  of  the  organism  to  the  environment  is  due  to  the  fact  that 
the  development  of  each  individual  is  molded  by  the  environment  so  as 
to  fit  it.  Thus  some  at  least  of  the  apparent  mystery  of  adaptations  is 
dispelled. 

When  we  think  of  the  fitness  of  the  organism  to  the  environment 
we  take  an  entirely  one-sided  view  of  the  matter,  for  if  the  organism 
fits  the  environment,  no  less  certainly  must  the  environment  fit  the 
organism.     This  idea  of  the  "fitness  of  the  environment"  has  been 

^  From  D.  S.  Jordan  and  V.  L.  Kellogg,  Evolution  and  Animal  Life. 

i88 


THE  BACKGROUND  OF  DARWINISM— ADAPTATIONS         189 

admirably  discussed  by  Professor  Lawrence  J.  Henderson  in  a  stimu- 
lating volume.^ 

Henderson  points  out  that  the  environment,  no  less  than  organ- 
isms, has  had  an  evolution.  The  particular  environmental  complex 
as  it  exists  today  is  absolutely  unique.  There  is  hardly  an  element  of 
the  effective  environment  that  could  be  changed  without  causing  the 
extinction  of  hfe  or  at  least  a  transformation  of  it  so  profound  that  it 
might  not  be  life  at  all  as  we  know  life.  Water,  for  example,  has  a 
dozen  unique  properties  that  condition  life.  Carbon  dioxide  could  not 
be  replaced  by  any  other  substance.  The  properties  of  the  ocean  are 
so  beautifully  adjusted  to  life  that  we  marvel  at  the  exactness  of  its 
fitness.  Finally,  the  chemical  properties  of  carbon,  hydrogen,  and 
oxygen,  the  most  abundant  elements,  are  equally  unique  and  unre- 
placeable.  In  brief,  given  the  environment  as  it  is,  life  could  not  be 
other  than  it  is.  The  evolution  of  the  environment  and  the  evolution 
of  organisms  have  gone  hand  in  hand,  or  perhaps  we  might  better  say 
hand  in  glove,  for  this  better  expresses  the  idea  of  mutual  fitness. 

Within  the  realm  of  the  general  environment  as  conceived  by 
Henderson  there  are  almost  innumerable  special  environments  due  to 
particular  combinations  of  the  various  environmental  units.  Within 
the  aquatic  environment,  for  example,  there  are  variations  such  as 
differences  in  salinity,  varying  from  extreme  saltiness  to  almost  total 
lack  of  salt;  there  are  inshore  conditions  and  open-sea  conditions;  there 
are  surface  conditions  and  those  at  relatively  great  depths;  and 
there  are  great  differences  due  to  temperature.  Similarly  on  land, 
there  are  surface  conditions,  subterranean  conditions,  caves,  deserts, 
forests,  plains,  mountains,  arctic,  tropical  conditions,  and  many  others. 
No  two  areas  on  land  are  precisely  similar  in  all  respects.  All  of  this 
makes  for  a  corresponding  multiplicity  of  animal  and  plant  forms.  In 
the  case  of  plants  the  action  of  the  environment  is  remarkably  direct; 
'for  the  plant  cannot  get  away  from  a  fixed  environment.  If  the 
environment  undergoes  material  change,  the  plant's  only  response  is  a 
structural  one.  For  example,  if  plants  that  are  accustomed  to  a  rela- 
tively humid  climate  are  grown  in  the  desert  they  develop  numerous 
xerophytic  adaptations  such  as  small  leaves  with  greatly  diminished 
transpiration  surface,  a  thick  epidermis,  hairs,  or  spines,  small  stature, 
deep-root  system,  and  other  similar  protections  against  the  inimical 
desert  conditions.     Similarly,  plants  accustomed  to  grow  in  relatively 

^  L.  J.  Henderson,  The  Fitness  of  the  Environment,  19 13. 


IQO      READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

dry  soil,  if  grown  in  soil  that  is  covered  over  with  water,  will  produce 
aquatic  leaves  and  roots  and  undergo  appropriate  changes  in  epidermis 
and  loss  of  supporting  tissues,  for  plants  that  are  buoyed  up  by  water 
need  little  support. 

Animals,  on  the  other  hand,  are  for  the  most  part  not  so  intimately 
related  to  a  local  environment  as  are  plants.  They  are  characteristi- 
cally mobile  creatures  with  varying  capacities  for  wandering  about  and 
selecting  the  habitat  that  best  suits  them. 

''By  virtue  of  being  unlike  or  possessing  different  properties," 
says  Shelford,^  ''the  various  animal  species  require  different  conditions 
for  the  best  adjustment  of  their  internal  processes.  For  example,  the 
carp  lives  in  shallow  and  muddy  ponds  and  rivers,  while  the  brook 
trout  lives  only  in  clear  swift  streams.  These  two  organisms  are  able 
to  move  about  and  find  places  to  which  they  are  suited.  The  differ- 
ences between  them  are  clearly  indicated  by  the  differences  in  the 
habitats  which  they  prefer. 

"By  observation  and  by  experimentation  it  has  been  shown  that 
animals  select  their  habitats.  By  this  we  do  not  mean  that  the 
animal  reasons,  but  that  selection  results  from  regulating  behavior. 
The  animal  usually  tries  a  number  of  situations  as  the  result  of  random 
movements,  and  stays  in  the  set  of  conditions  in  which  its  physiological 
processes  are  least  interfered  with.  This  process  is  called  selection  by 
trial  and  error.  If  animals  are  placed  in  situations  where  a  number  of 
conditions  are  equally  available,  they  will  almost  always  be  found  liv- 
ing in  or  staying  most  of  the  time  in  one  of  the  places.  The  only 
reason  to  be  assigned  for  this  unequal  or  local  distribution  of  the  ani- 
mals is  that  they  are  not  in  physiological  equilibrium  in  all  the  places. 
However,  some  animals  move  about  so  much  that  it  is  with  some 
difficulty  that  we  determine  what  their  true  habitats  are." 

This  idea  of  habitat  preference  and  habitat  selection  is  extremely 
important  for  a  correct  understanding  of  adaptation,  or  the  fitness  of 
organisms  to  environments.  Much  of  the  observed  fitness  may  be  due 
to  the  fact  that  an  organism  has  chosen  out  of  a  wide  range  of  environ- 
ments the  one  that  best  suits  it.  We  cannot  in  such  a  case  say  that  the 
environment  has  had  a  direct  influence  in  shaping  the  organism  any 
more  than  we  could  say  that,  when  a  man  tries  on  various  shoes  and 
finds  a  pair  to  fit,  he  has  been  responsible  for  the  fitness  of  the  shoes. 

Many  special  adaptations  may  be  explained  through  habitat 
choice.     Thus  animals  such  as  the  duckbill  platypus,  the  lung-fishes, 

^  V.  E.  Shelf ord,  Animal  Communities  in  Temperate  America  (1913). 


THE  BACKGROUND  OF  DARWIxNISM— ADAPTATIONS  191 

and  others  whose  teeth  are  replaced  by  bony  or  chitinous  plates  that 
are  used  for  crushing  the  hard  shells  of  molluscs  and  crustaceans,  may 
not  confidently  be  said  to  have  developed  these  crushing  appliances 
and  to  have  abandoned  the  use  of  teeth  in  adaptation  to  a  habit  of 
feeding  upon  hard-shelled  prey;  but  rather  it  seems  more  likely  that  the 
loss  of  teeth  and  the  development  of  crushers  occurred  through  a 
degenerative  process  incident  to  racial  senescence  and  that  the  pos- 
session of  the  crushing  equipment  enabled  them  to  avail  themselves  of 
a  new  type  of  food,  formerly  unavailable  to  them. 

The  organic  environment. — In  his  admirable  chapter  entitled 
''The  Web  of  Life,"  which  we  shall  quote  entire.  Professor  Thomson 
has  given  us  a  vivid  picture  of  vast  systems  of  interdependencies  that 
exist  throughout  the  organic  world.  No  species,  no  creature,  lives  to 
itself  alone;  it  is  intimately  tied  up  with  a  host  of  other  creatures  with 
interwoven  destinies.  Thus  one  species  of  animal  is  adapted  to  live 
upon  certain  plants  or  other  animals,  which  in  turn  may  be  dependent 
upon  still  other  animals  or  plants.  The  elimination  of  one  species  may 
cause  the  elimination  or  the  radical  change  of  a  dependent  species. 
We  cannot  afford  ever  to  forget  this  great  truth  of  the  oneness  of 
nature.     It  is  the  keynote  of  life  and  of  evolution. 

Adaptation  due  partly  to  functional  activity. — It  is  a  commonplace 
which  needs  no  special  demonstration  to  say  that  organs  improve 
through  use  and  deteriorate  through  disuse.  Many  organs,  then, 
which  in  the  adult  condition  appear  to  us  to  be  so  admirably 
adapted  to  perform  certain  duties,  must  be  thought  of  as  having  been 
gradually  molded  by  functioning  during  the  entire  period  of  individual 
development.  If  the  motor  nerve  running  to  a  limb  bud  of  a  growing 
embryo  be  severed  at  an  early  stage  and  no  secondary  nerve  connection 
be  established,  the  limb  will  continue  to  grow  up  to  a  certain  point,  but, 
in  its  paralyzed  condition,  will  be  incapable  of  exercising  its  functions 
and  will  cease  to  develop.  A  certain  amount  of  development  will 
therefore  be  seen  to  be  independent  of  functioning,  but  full  develop- 
ment of  functional  efficiency  is  obtained  only  through  functioning. 

''The  relation  between  structure  and  function  in  an  organism," 
says  Professor  Child,^  "is  similar  in  character  to  the  relation  between 
the  river  as  an  energetic  process  and  its  banks  and  channel.  From  the 
moment  that  the  river  began  to  produce  structural  configurations 
in  its  environment,  the  products  of  its  activity  accumulated  in  certain 

^  C.  M.  Child,  "Regulatory  Processes  in  Organisms,"  Jour.  Morp/i.,  Vol. 
XXII  (1911). 


192      READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

places  and  modified  its  flow It  moulds  its  banks  and  bottom, 

forming  here  a  bar,  there  an  island,  here  a  bay,  there  a  point  of  land, 
but  still  flowing  on,  though  its  course,  its  speed,  its  depth,  the  character 
of  the  substances  which  its  carries  in  suspension  or  in  solution,  all  are 
altered,  built  up  by  its  own  past  activity."     According  to  this  view, 
structure  is  simply  the  resultant  of  the  interaction  of  function  and 
environment,  of  functional  activity.     Though  perhaps  a  little  extreme 
for  most  of  us,  this  view  is,  we  beUeve,  essentially  correct.     We  are 
prone  to  overemphasize  structure  in  our  discussions  of  adaptation 
and  evolution  and  to  lay  too  little  stress  upon  the  energy  side   of 
development.     Certainly  no  structure  is  ever  formed  without  proto- 
plasmic activity  of  a  very  definite  sort,  and  in  this  sense  adaptations 
are  to  be  thought  of  as  the  results  of  functioning.     Why,  then,  do  we 
claim  to  be  astonished  at  the  effective  way  in  which  certain  organs 
accompUsh  their  functions,  when  functioning  has  taught  them  their 
task  ? 

LAWS    OF   ADAPTATION 

Adaptations  have  been  variously  classified  by  different  writers. 
Perhaps  the  most  significant  classification  is  that  of  Osborn,  which 
is  based  on  their  supposed  evolutionary  origin.  According  to  this 
writer  and  others  there  are  two  categories  of  adaptations  to  environ- 
mental conditions:  the  first  has  to  do  with  the  tendency  of  unrelated 
species  to  assume  similar  structures  under  similar  environmental 
conditions;  the  second  has  to  do  with  the  tendency  of  related  species 
to  assume  dift'erent  adaptive  structures  under  different  environmental 
conditions.  In  both  categories  the  environment  appears  to  be  the 
determining  factor. 

(i)  A  good  example  of  the  first  category,  which  illustrates  wh^t 
Osborn  calls  "the  law  of  convergence  or  parallelism  of  form,"  is  seen 
in  the  tendency  of  many  aquatic  types  of  vertebrates  to  assume  the 
fishlike  form.  As  is  well  shown  in  Fig.  40,  the  shark  (a  fish),  the 
ichthyosaur  (an  extinct  aquatic  reptile),  and  the  porpoise  (a  marine 
mammal),  all  possess  the  same  fusiform  body  best  adapted  for  speed 
under  water,  the  same  types  of  locomotor  structures,  consisting  of  the 
great  propeller  fin  (caudal  fin)  and  the  steering  and  balancing  fins, 
the  dorsal  fins  and  paired  fins.  Apart  from  these  superficial  adapta- 
tions for  swift  locomotion  in  the  water,  the  three  types  are  pro- 
foundly different.  The  shark  breathes  with  gills,  the  reptile  and 
mammal  with   lungs,   the   fish   and   reptile   are   cold-blooded,   the 


THE  BACKGROUND  OF  DARWINISM— ADAPTATIOXS  i 


93 


Fig.  40. — Three  aquatic  types  of  vertebrate,  to  illustrate  convergent  adapta- 
tion of  three  wholly  unrelated  forms  of  marine  life.  All  three  show  the  fusiform 
body,  median  and  paired  fins,  though  the  skeletal  structures  are  radically  differ- 
ent. A,  shark  (Pisces);  B,  ichthyosaur  (Reptilia);  C,  porpoise  (Mammalia). 
{From  Newman^  after  Osborn.) 


194      READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

mammal  warm-blooded.  The  internal  anatomy  of  the  three  differs 
fundamentally  in  every  detail. 

A  list  of  other  types  of  convergence  will  more  adequately  illustrate 
the  law. 

Flying  and  parachuting  animals  occur  among  nearly  all  vertebrate 
and  some  invertebrate  classes.  Planes  of  some  sort  are  found  for 
supporting  the  body  in  the  air.  The  plane  is  made  in  various  ways 
in  different  groups,  but  functions  much  the  same  in  all  of  them. 

Running  animals  of  various  classes  have  long  legs,  and  a  tendency 
to  stand  on  the  toes.  There  is  also  in  several  unrelated  groups  the 
tendency  to  reduce  the  number  of  toes,  the  culmination  of  which  is 
seen  in  the  one-toed  horses. 

Climbing  animals  are  all  provided  with  clinging  appendages  of 
some  sort,  including  such  structures  as  hooked  claws,  prehensile 
fingers  or  tail,  suction  pads  on  the  feet,  and  other  similar  adaptations. 

Burrowing  animals  have,  as  a  rule,  extra-heavy  shoulder  girdle 
and  strong  fore  limbs  with  heavy  gouging  claws.  Many  of  them  also 
are  blind  or  nearly  so,  as  befits  life  in  dark  underground  passages. 

Desert-dwelling  animals  as  a  rule  are  provided  with  heavy 
scales,  spines,  or  armor,  to  prevent  excessive  loss  of  moisture  and  as  a 
protection  against  spiny  plants.  They  also  usually  have  burrowing 
habits  enabling  them  to  escape  the  extremes  of  heat  and  cold. 

Cave  animals  are  usually  blind  or  nearly  so  and  are  relatively 
pale  in  color,  sometimes  without  any  pigmentation. 

Deep-sea  animals  of  many  sorts  have  phosphorescent  orgains  by 
means  of  which  they  either  attract  their  prey  or  find  their  way  about 
the  dark  sea  floor.  Some  of  these  organs,  called  "lanterns,"  can  be 
used  as  searchlights.  The  eyes  of  deep-sea  fish  are  either  enormously 
large  or  are  "telescope  eyes,"  adapted  for  sensing  light  of  low 
intensities. 

Ant-eating  animals,  belonging  to  several  distinct  groups,  are 
heavily  armored  against  the  attacks  of  ants,  have  strong  claws  for 
digging  up  ant  galleries,  have  long  snouts  or  beaks  with  a  long  sticky 
tongue  for  capturing  ants,  and  an  arrangement  of  the  glottis  to  prevent 
ants  from  crawling  into  the  lungs. 

2.  There  are  almost  innumerable  examples  of  the  law  of  divergence 
of  form,  which  is  called  also  the  law  of  adaptive  radiation.  Almost 
every  successful  class  or  order  of  vertebrate  animals,  for  example, 
has  members  that  have  adjusted  themselves  to  all  of  the  main  modes 
of  living.     Thus  among   lizards,  for   example,   there  are  primitive 


THE  BACKCxROUND  OF  DARWINISM— ADAPTATIONS         195 

running  forms  that  prefer  the  surface  Kfe  and  swift  motion;  subter- 
ranean burrowing  types  that  sometimes  are  limbless  like  snakes,  and 
are  blind;  many  arboreal  or  climbing  types;  a  few  volant  or  flying 
types;  a  few  ant-eating  types;  and  several  more  or  less  completely 
aquatic  types.  Each  of  these  types  has  the  customary  adaptations 
for  its  own  mode  of  life. 

We  see,  then,  that  whether  divergent  structures  are  molded  into  a 
semblance  of  similarity  to  fit  a  definite  environment,  or  whether 
similar  structures  are  modified  in  diverse  ways  to  fit  various  divergent 
environments,  the  adaptation  is  related  very  definitely  to  the  environ- 
ment and  to  the  functional  life  of  the  organism.  No  wonder,  then, 
that  so  many  biologists  consider  that  the  ehvironment  has  been  a 
molding  force  in  the  evolution  of  adaptations. 

One  of  the  most  interesting  discussions  of  adaptations  is  that  of 
Weismann,  who,  it  appears,  is  greatly  impressed  with  the  uni- 
versality of  adaptation.  His  thesis  apparently  is  that  if  we  had 
complete  knowledge  of  the  field  of  biology,  we  would  discover  that 
everything  is  adaptive,  and  that  many  structures  or  habits  that  now 
appear  to  us  useless  or  non-adaptive,  would  be  found  to  have  a  definite 
value  to  the  organisms  possessing  them.  Some  authors  take  the 
opposite  extreme  and  claim  that  adaptation  has  been  merely  read  into 
a  vast  number  of  so-called  adaptive  structures  and  that  when  these 
structures  shall  have  been  adequately  investigated  they  will  be  found 
to  lack  the  value  imputed  to  them  by  uncritical  observers.  Some- 
where between  these  extreme  views  lies  the  truth. 

Thus  we  see  that  a  certain  amount  of  adaptation  is  inevitable  and 
needs  only  a  formal  physiological  explanation.  The  fitness  of  the 
environment,  habitat  selection,  and  the  relationship  that  exists 
between  function  and  structure,  are  adequate  explanations  for  the 
general  fact  of  adaptation  and  thus  take  away  much  of  the  mystery  that 
has  shrouded  the  concept  of  fitness.  There  are,  however,  very  many 
types  of  special  adaptation  which  do  not  yield  so  readily  to  the  general 
explanation  given.  Some  of  the  most  important  of  these  will  be  de- 
scribed below. 

ADAPTATIONS   CLASSIPIED 

Adaptations  are  variously  classified  by  different  authors,  and  that 
of  Jordan  and  Kellogg  is  as  good  as  any:  "  {a)  food-securing;  {b)  self- 
defense;  (c)  defense  of  young;  {d)  rivalry;  (e)  adjustment  to  sur- 
roundings." 


196      READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

Some  very  common  adaptations  may  belong  to  several  of  these 
categories  at  once.  Thus  the  sharp  teeth  and  hooked  claws  of  car- 
nivorous mammals  serve  equally  well  for  food-securing,  for  self- 
defense,  for  defense  of  young,  and  for  rivalry.  Similarly,  the  horns 
of  deer  and  other  ungulates  are  equally  adapted  for  self-defense, 
defense  of  young,  and  rivalry. 

There  can  be  no  especial  advantage,  in  this  connection,  in  present- 
ing a  detailed  review  of  adaptations  of  the  sorts  given  in  the  foregoing 
classification;  therefore  we  shall  confine  our  efforts  to  a  description 
of  a  few  typical  adaptations  about  which  the  greatest  controversy 
has  raged. 

SOME   SPECIAL  ADAPTATIONS 

The  electric  organ  of  the  torpedo,  a  widely  distributed  elasmo- 
branch  fish,  consists  of  a  sort  of  honeycomb-like  structure  on  each  side 
of  the  head.  This  structure  acts  as  a  storage  battery  and  is  capable 
of  storing  up  electricity  of  considerable  voltage.  The  animal  is 
capable  of  giving  a  very  distinct  shock  to  an  attacker  and  can  thus 
defend  itself  quite  effectively.  There  is  also  an  electric  eel,  native  to 
the  waters  of  Paraguay  and  Brazil,  that  is  able  to  give  severe  shocks  to 
bathers  or  to  horses  driven  through  the  streams.  A  type  of  catfish 
native  to  the  river  Nile  has  a  similar  electric  equipment.  In  all  of 
these  cases  the  storage  battery  is  made  up  of  modified  voluntary 
muscles  and  is  of  considerable  size. 

The  mammary  glands  of  mammals  are  skin  glands  usually  with 
well-defined  ducts  leading  to  the  surface  and  terminating  in  teats. 
These  glands  are  quite  voluminous  and  serve  admirably  the  purpose  of 
feeding  new-born  young  until  the  latter  are  able  to  use  the  more  varied 
food  normal  to  the  adult.  In  the  lowest  mammals,  the  monotremes 
or  egg-laying  mammals,  these  glands  are  relatively  poorly  developed 
and  diffuse;  also  they  are  known  to  be  developed  through  a  regional 
specialization  of  sweat  glands.  In  the  true  mammals  or  Eutheria  the 
glands  are  modified  sebaceous  or  oil  glands  and  may  be  seen  to  develop 
from  the  same  embryonic  rudiments  as  the  latter. 

The  marsupial  pouch  of  the  kangaroo  and  its  allies  is  a  pocket- 
like fold  of  the  integument,  folded  forward  or  backward  over  the  region 
of  the  abdomen  in  which  are  located  the  mammary  glands.  This 
pouch  is  used  as  a  shelter  for  the  tiny  immature  larval  foetuses. 
Hartmann  has  recently  described  a  very  striking  piece  of  behavior  in 
connection  with  the  birth  of  young  opossums.     The  young  are  born 


THE  BACKGROUND  OF  DARWINISM— ADAPTATIOXS         197 

in  an  exceedingly  immature  state  and  looking  like  tiny  pink  grubs. 
They  crawl  under  their  own  power,  by  means  of  a  swimming-like 
motion,  through  the  hairs  of  the  mother's  abdomen,  till  they  reach  the 
pouch.  This  they  enter  unaided  and  each  tiny  larva  finds  for  itself 
a  slender  tubular  teat,  which  it  swallows  and  holds  in  place  by  a 
specially  adapted  hold-fast  mouth.  The  young  remains  attached 
fixedly  to  this  teat  for  some  weeks,  feeding  almost  constantly  on  milk. 
After  a  long  interval  the  teat  is  released,  the  mouth  metamorphoses 
into  the  adult  form  and  the  young  feeds  only  at  intervals,  as  do  the 
young  of  other  mammals.  This  complex  of  adaptive  structures  and 
instincts  is  among  the  most  remarkable  in  the  annals  of  biology. 

Nest-making  instincts  in  birds  represent,  on  the  behavior  side, 
adaptations  of  extraordinary  perfection.  Some  nests  are  built  with 
the  greatest  care  and  precision,  others  represent  a  relatively  crude  and 
slovenly  performance.  Some  nests  are  made  of  twigs,  fibres,  and  mud, 
others  of  mud  alone,  still  others  are  hollowed  out  in  clay  or  sand  banks, 
and  some  are  made  in  holes  in  the  ground.  In  any  case,  the  type  of 
nest  is  highly  specific  and  due  to  a  hereditary  instinct;  for  birds 
receive  no  instruction  in  nest-making. 

Before  bringing  to  a  close  this  brief  list  of  particularly  noteworthy 
adaptations  let  us  recall  to  mind  the  series  of  special  adaptations  listed 
as  examples  of  the  laws  of  adaptation,  such  as  aquatic,  arboreal,  cur- 
sorial, flying,  burrowing,  ant-eating,  and,  especially,  adaptations  of 
deep-sea  animals. 

PARASITISM  AND   DEGENERATION 

A  vast  number  of  animals  and  plants  have  given  up  the  active" 
search  for  food  and  have  taken  up  the  relatively  easy  habits  of  para- 
sitism. In  adaptation  to  this  life  certain  structures  have  developed 
and  many  of  the  characters  found  in  independent,  free-roving  crea- 
tures have  disappeared  or  become  reduced  to  mere  vestiges.  Thus 
the  more  completely  dependent  or  parasitic  an  animal  becomes,  the 
more  completely  does  it  lose  its  organs  of  locomotion  and  its  sense 
organs  such  as  eyes,  auditory  organs,  tentacles,  etc.  Some  animals 
are  free-living  when  young  or  in  the  larval  condition  and  only  settle 
down  to  a  parasitic  Hfe  when  near  the  end  of  the  life-cycle;  other 
animals  are  parasitic  only  when  young  or  larval  and  become  inde- 
pendent in  the  adult  condition;  still  others  are  parasitic  throughout 
the  entire  life-cycle  and  pass  from  host  to  host  without  any  interval 
of  independent  life.  Some  of  these  complete  parasites  pass  one  phase 
of  the  life-cycle  on  one  species  of  host  and  the  remainder  on  another 


igS     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

species  of  host.  Thus  the  liver  fluke  in  the  adult  condition  lives  in  the 
gall  bladder  of  the  sheep,  while  the  early  larvae  live  within  the  body 
cavities  of  a  species  of  land  snail.  The  transfer  from  host  to  host  in 
this  case  must  be  a  procedure  involving  many  chances  of  failure  to  a 
very  few  chances  of  success,  and,  in  adaptation  to  these  vicissitudes, 
the  number  of  eggs  and  larvae  produced  by  a  single  adult  individual 
runs  up  into  the  milUons. 

The  classic  case  of  extreme  parasitic  degeneration  is  that  of 
Sacculina.  The  young  larva  of  Sacculina  is  a  typical  entomostracan 
crustacean  larva  which  swims  about  and  leads  a  free  life  for  a  time, 
but  soon  attaches  itself  by  means  of  its  antennae  to  a  hair  pit  of  a  crab, 
a  small  hole  in  the  latter's  armor.  The  internal  tissues  of  the  larva 
then  undergo  degenerative  processes  and  are  reduced  to  an  almost 
fluid  mass  of  embryonic  cells,  which  flow  through  the  hair  pore  of  the 
crab,  and  into  the  latter's  lymph  spaces.  The  small  mass  of  cells  then 
rounds  up  and  is  carried  about  with  the  circulation  of  the  crab's  blood 
until  it  comes  to  a  favorable  place  of  lodgment,  usually  the  wall  of  the 
intestine  just  back  of  the  stomach.  Here  it  flattens  out  and  sends 
rootlike  branches  almost  all  over  the  crab's  body,  like  a  malignant 
tumor  in  its  invasion  of  foreign  tissues.  The  unbranched  part  of  the 
parasite  is  little  more  than  a  sac  of  reproductive  organs,  and  these 
produce  eggs  and  sperms,  which  unite  to  produce  larvae.  By  this 
time  the  host  is  killed  and,  with  the  decay  of  its  body,  the  larvae  escape 
into  the  sea  water  ready  for  a  brief  period  of  free  life  before  attacking 
another  host. 

Almost  every  group  of  animals  and  most  of  the  groups  of  plants 
have  their  parasitic  representatives  and  every  degree  of  parasitism 
and  the  accompanying  degenerative  changes  are  to  be  found.  Of 
course,  it  is  an  open  question  whether  parasitism  causes  degeneration 
or  whether  degenerating  creatures  take  refuge  in  parasitism;  but  in 
either  case  the  adaptive  features  of  the  situation  are  obvious. 

Commensalism. — If  parasitism  be  defined  as  an  association 
between  two  organisms  in  which  one  (the  parasite)  lives  at  the  expense 
of  and  to  the  detriment  of  the  other  (the  host),  commensalism  may  be 
defined  as  an  association  in  which  the  two  organisms  exist  in  close 
association  without  any  positive  detriment  to  either.  In  some  cases 
the  claim  is  made  that  the  association  is  mutually  beneficial,  but  as  a 
rule  the  condition  is  relatively  one-sided. 

An  interesting  example  of  commensalism  is  that  of  the  sea  cucum- 
ber and  the  little  fish  Fierasfer.     This  strange  little  animal  inhabits 


THE  BACKGROUND  OF  DARWINISM— ADAPTATIONS 


199 


the  rectum  of  the  sea  cucumber  and  may  be  seen  to  He  with  only  its 
head  out.  From  this  shelter  it  darts  forth  to  capture  its  prey;  which 
done,  it  returns  to  its  shelter. 
Curiously  enough  the  vent 
of  the  little  fish  is  situated 
just  back  of  its  mouth  so 
that  its  wastes  may  be 
voided  when  in  its  usual 
position.  There  can  be  no 
advantage  to  the  sea  cu- 
cumber in  such  an  arrange- 
ment,  though  no  particular  ^,^p>^^     -idS#l?^-    --  --^'-''^rvi'^B.'     .• 

harm  is  done.    Another  case  ^^^*K^  ;  ^  :  ^  T "  "\' ""  ^^^C  "^ '-, 

of  this  sort  is  that  of  several  sm^'-^  \  '    >....,„fic«;dU.iiri  .-> . ,  ^'r^^ 

species  of  Remora  which 
attach  themselves  by  a  large 
diskoid  adaptation  on  top  of  Fig.  41. — Fierasfer  acus,   penetrating   the 

the  head  to  various  fish  such     ^S""^  openings  of  holothurians,  I  natural  size. 

{troni  Boiiienger,  ajtcr  Emery.) 

as   sharks,  barracudas,  etc. 

The  sucking  disk  is  a  modified  dorsal  fin.  The  remora  merely  gains 
free  transportation  to  more  favorable  feeding-grounds.  When  the 
desired  food  is  sighted  the  passenger  leaves  its  conveyance  tempo- 
rarily, but  returns  by  a  sudden  swift  dash  and  resumes  its  hold. 
The  shark  gets  nothing  except  perhaps  the  sense  of  companionship, 
and  is  also  undoubtedly  somewhat  hindered  in  its  locomotion. 

Some  of  the  most  remarkable  cases  of  commensalism  are  found  in 
connection  with  elaborate  colonies  of  ants.  In  some  cases  two  species 
of  ants  live  together  in  the  relationship  of  masters  and  slaves.  The 
master  species  is  unable  to  perform  any  of  the  ordinary  duties  of  the 
colony,  such  as  securing  food,  taking  care  of  young,  etc.  In  extreme 
cases  the  masters  are  only  soldiers,  specialized  for  fighting  and  maraud- 
ing, and  cannot  even  feed  themselves  unaided.  The  slave  species 
would  be  able  to  carry  on  to  some  extent  if  not  captured,  but  thrives 
exceptionally  well  under  the  protection  of  the  soldier  species.  There 
are  among  ants  many  varieties  of  commensal  relationship  less  extreme 
than  this,  but  this  will  serve  as  a  typical  case. 

Communal  life. — Among  the  higher  insects  and  higher  vertebrates, 
especially  among  the  ants  and  bees,  we  find  a  very  elaborate  social  life. 
In  ants,  for  example,  the  typical  colony  consists  of  a  queen  (the  only 
fertile  female  in  the  colony),  several  males  (mates  of  the  queen). 


200      READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

• 

ordinary  workers  (sterile  females  of  the  first  type),  soldiers  (sterile 
females  of  the  second  type),  and  sometimes  officers  (especially  large 
and  powerful  sterile  females  that  seem  to  direct  the  line  of  march  in 
legionary  ants).  All  of  these  casts  are  produced  from  the  eggs  of  one 
female  and  are  the  result  of  various  special  diets  permitted  the  larvae 
by  the  workers.  Among  bees,  similarly,  there  is  one  queen,  a  number 
of  drones  (males),  and  the  sterile  female  workers,  who  perform  the 
functions  of  nursing  the  larvae,  cleaning  up  the  hive,  collecting  pollen 
and  nectar,  and  making  honey  and  wax.  Detailed  accounts  of  the 
lives  of  bees  have  been  given  by  various  authors,  notably  by  Maeter- 
linck in  his  Life  of  the  Bee. 

COLOR   IN   ANIMALS 

''The  phenomena  of  color  in  both  animals  and  plants,"  says 
Metcalf,^  "are  among  the  most  remarkable  and  interesting  in  the 
whole  realm  of  nature.  It  is  not  so  much  the  way  in  which  the  color 
is  produced,  whether  by  pigments  or  by  refraction,  that  interests  us 
in  this  connection,  as  it  is  the  uses  to  which  colors  are  put.  Let  us 
first  refer  to  the  colors  of  animals. 

"According  to  the  uses  to  which  colors  in  animals  are  put,  we 
may  classify  them,  for  purposes  of  description,  as  follows: 

"Indifferent  coloration,  not  useful,  so  far  as  we  can  judge; 

Colors  of  direct  physiological  value; 

Protective  coloration  and  resemblances; 

Aggressive  coloration  and  resemblances; 

Alluring  coloration  and  resemblances; 

Warning  coloration; 

Immunity  coloration; 

Mimetic  coloration  and  resemblances; 

A.  Protective 

B.  Aggressive 

Signals  and  recognition  marks; 
Confusing  coloration; 
Sexual  coloration." 

A  few  examples  of  these  categories  of  animal  coloration  will  serve 
to  illustrate  the  ways  in  which  they  are  believed  to  be  adaptive  and 
thus  better  to  fit  the  organism  for  its  struggle  for  existence. 

Protective  resemblance. — Many  animals  that  live  at  or  near  the 
surface  of  the  sea  are  practically  transparent.     Fishes  are  commonly 

^  M.  M.  Metcalf,  Organic  Evolution  (191 1). 


THE  BACKGROUND  OF  DARWINISM— ADAPTATIONS         201 

dark-colored  above  and  light-colored  below,  so  that  to  the  enemy  above 
they  blend  with  the  dark  bulk  of  the  water  and  to  the  enemy  below 
they  are  hidden  by  the  fact  that  the  shadow  cast  by  their  own  bulk  is 
sufficiently  neutralized  by  the  ventral  light  coloring  to  render  them 
inconspicuous. 

A  very  large  number  of  arboreal  animals  are  green ;  such  as  grass- 
hoppers, leaf  hoppers,  spiders,  green  lizards,  parrots,  etc.  Prairie  and 
desert  animals  are  usually  dull-colored  like  their  surroundings.  IVIany 
butterflies  are  brightly  colored  like  the  flowers  upon  which  they  feed. 
Many  arctic  animals  are  white  like  their  snowy  background. 

Some  animals,  like  the  chameleon  and  the  flounder,  change  their 
colors  so  as  to  keep  in  harmony  with  changing  backgrounds. 

There  are  many  cases  of  protective  resemblance,  involving  both 
form  and  color,  between  an  organism  and  some  particular  feature  of  its 
environment.  The  walking-stick  insect  is  long  and  slender  and  colored 
like  a  twig.  Many  caterpillars  when  disturbed  stand  out  stiff  and 
straight  like  leafless  twigs.  A  species  of  sea-horse  (a  teleost  fish)  has 
its  fins  fringed  out  into  structures  that  closely  resemble  the  fronds  of 
seaweed  in  which  the  animal  lives.  Many  insects,  belonging  to 
several  orders,  have  very  striking  resemblances  to  leaves.  The  case  of 
Kallima  (Fig.  42),  the  dead-leaf-butterfly  is  a  classic  example  of  this 
type  of  protective  resemblance.  The  resemblance  is  so  nearly  perfect 
that,  when  one  has  mounted  specimens  of  butterfly  and  leaf  before  him, 
he  has  to  examine  them  closely  to  detect  the  fraud.  The  details  of  the 
leaf  color,  veins,  petiole,  marginal  notches,  even  wormholes,  so  common 
in  dead  leaves,  are  reproduced  in  the  butterfly's  wings.  Many  tree- 
frogs  have  a  leaf-shaped  pattern  bordered  with  black  to  resemble  the 
shadow  cast  by  a  leaf.  These  are  only  a  few  scattering  examples  of  an 
exceedingly  prevalent  type  of  adaptation. 

Aggressive  coloration  and  resemblance. — There  is  a  close  simi- 
larity between  this  phenomenon  and  the  one  just  dealt  with,  but 
instead  of  being  used  defensively,  it  is  used  offensively,  in  that  it 
enables  the  predaceous  animal  to  remain  hidden  from  its  prey.  Tlius 
the  polar  bear  and  the  arctic  fox  are  white  and  therefore  inconspicuous 
to  seals  and  arctic  birds,  their  prey.  Perhaps  the  most  striking 
instance  of  this  type  of  coloration  is  that  of  the  tiger,  whose  tawny 
coat  and  dark  stripes  resemble  the  reeds. and  their  vertical  shadows 
in  the  jungle. 

Alluring  coloration  and  resemblance. — 'Tn  India,"  says  Metcalf, 
''there  is  a  Mantis  (insect)  which  in  shape  and  color  resembles  an 


202      READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

orchid  blossom.  It  deceives'  butterflies  and  other  insects,  which  it 
captures  as  they  approach  the  seeming  flower.  In  Java  there  is  a 
spider  which  resembles  a  bit  of  bird  excrement  upon  which  butterflies 
are  so  apt  to  light.  This  resemblance  enables  it  to  capture  the 
butterflies  upon  which  it  feeds." 


Fig.  42. — Kallima,  the  ''dead-leaf  butterfly."     (From  Jordan  and  Kellogg.) 


Warning  coloration. — Many  animals  that  are  for  various  reasons 
harmful  or  dangerous  to  other  animals  have  strikingly  distinct  color 
patterns  which  have  been  interpreted  by  some  authors  as  warning 
marks  to  keep  off  possible  attackers.  Bees,  wasps,  hornets,  some 
poisonous  snakes,  many  spiders,  all  of  which  have  stings  or  fangs,  are 
marked  with  bands  of  contrasting  colors.     Other  animals  that  are 


THE  BACKGROUND  OF  DARWINISM— ADAPTATIONS         203 

nauseous  if  eaten,  still  others,  like  the  skunk  and  his  tribe,  that  pro- 
duce offensive  odors,  have  well-defined  markings  that  are  classed  as 
examples  of  warning  coloration. 

Immunity  coloration. — Professor  Reighard  has  taken  exception 
to  the  interpretation  of  conspicuous  coloration  as  warning  adaptations. 
His  theory  of  "immunity  coloration"  furnishes  an  alternative  interpre- 
tation which  appears  less  open  to  criticism.  According  to  this  idea 
well-protected  animals  are  relatively  safe  from  attack  and  therefore 
may  become  conspicuous  without  endangering  themselves.  They  are 
immune  and  therefore  their  conspicuous  markings  may  be  merely  the 
result  of  color  run  riot  without  any  check  on  the  part  of  natural 
selection. 

Mimicry. — This  is  a  special  type  of  protective  coloration  in  which 
an  otherwise  defenseless  species  has  a  striking  resemblance  to  some 
well-protected  species  with  warning  coloration.  Thus  wasps  and  bees 
are  "mimicked"  by  flies,  beetles,  and  moths.  They  enhance  the 
resemblance  by  similarities  of  behavior  and  habitat.  Ants  are  pro- 
tected by  the  fact  that  they  contain  formic  acid,  which  is  distasteful 
to  most  animals  (though  some  animals  feed  very  largely  on  them). 
Consequently  there  are  many  ant  mimics  belonging  to  several  orders 
of  insects  and  to  spiders.  In  some  cases  these  ant  mimics  are  inhabit- 
ants of  ant  colonies  and  succeed  in  passing  themselves  off  as  ants  even 
among  the  ants  themselves.  The  classic  cases  of  mimicry,  however, 
are  those  in  which  certain  species  of  edible  butterflies  are  said  to 
mimic  other,  unrelated,  nauseous  species  of  butterflies. 

It  is  very  difficult  to  distinguish  the  model  from  the  mimic  except 
by  careful  anatomical  examination  which,  of  course,  could  not  be 
applied  in  nature.  It  should  be  said  about  mimicry,  however,  that  it 
would  work  only  in  case  the  mimic  occurs  in  much  smaller  numbers 
than  the  model,  and  that  the  two  species  occupy  the  same  regions  at 
the  same  time.  Some  critics  have  claimed  that  these  conditions  do 
not  prevail  in  all  cases.  If  their  contention  is  valid,  the  usual  expla- 
nations of  mimicry  need  revision.  Cases  of  aggressive  mimicry  are 
noted  among  certain  predaceous  animals,  such  as  spiders  which  mimic 
flies  and  ants,  and  are  therefore  able  to  approach  their  prey  more 
effectively. 

Signals  or  recognition  marks. — The  common  cotton-tail  rabbit 
raises  its  white  tail  when  it  runs.  This  is  interpreted  as  a  signal  of 
danger  to  other  rabbits.  Some  antelopes  have  a  conspicuous  white 
rump  which  is  supposed  to  be  a  danger  signal.     Many  distinct  specific 


204      READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

markings  such  as  the  red  heads  of  woodpeckers,  distinct  white  or  black 
bars  on  the  wings  of  other  birds,  may  serve  for  recognition  purposes 
within  the  species. 

Confusing  coloration. — Many  butterflies  and  moths,  and  not  a 
few  birds  have  rather  conspicuous  markings  when  in  flight,  which  may 
serve  as  specific  recognition  marks;  but  when  they  alight  after  a 
zigzag  course  through  the  air,  they  cover  up  the  conspicuous  markings 
and  blend  with  the  background  in  various  ways.  They  are  supposed 
to  alight  when  in  danger  of  capture  and  they  apparently  disappear, 
much  to  the  confusion  of  the  pursuer.  Thus  Kallima,  the  dead-leaf 
butterfly,  is  quite  conspicuous  from  above  while  in  flight,  but  when  it 
alights,  it  cannot  be  distinguished  from  a  dead  leaf. 

Sexual  coloration. — A  great  many  groups  of  animals  exhibit  a 
pronounced  sexual  dimorphism  in  color  and  pattern.  The  most 
conspicuous  instance  of  this  is  that  of  birds  among  which  the  female 
is  usually  protectively  colored  so  as  to  be  inconspicuous  when  on  the 
nest  or  when  sheltering  the  young,  while  the  male  of  the  same  species 
is  frequently  conspicuously  colored.  Similar  situations  are  found 
among  butterflies  and  moths  in  which  sometimes  one  sex  and  some- 
times the  other  is  the  more  elaborately  colored.  Sexual  coloration  is 
also  common  among  teleost  fishes,  lizards,  spiders,  and  many  other 
groups.  Charles  Darwin  devised  a  special  "sexual  selection"  theory 
to  account  for  just  this  type  of  adaptation. 

One  more  kind  of  coloration  that  is  not  specifically  dealt  with  by 
Metcalf  is  what  has  now  come  to  be  known  as  "camouflage. "  Many 
animals  when  viewed  out  of  their  environment  appear  to  be  very 
conspicuous  owing  to  the  juxtaposition  of  patches  of  irregular  colors. 
In  their  natural  surroundings,  however,  they  become  practically 
invisible.  Thus  the  nighthawk  with  its  strongly  contrasted  patterns 
almost  fades  from  view  against  the  bark  of  a  tree. 

For  excellent  illustrations  of  animal  colorations  the  reader  is 
referred  to  Professor  Metcalf's  book  Organic  Evolution,  where  he  has 
gathered  together  in  color  plates  many  of  the  finest  examples  of  the 
phenomena  under  discussion. 

General  considerations. — Adaptations  are  characteristic  of  all 
living  organisms  and  must  be  accounted  for  by  any  evolutionary  theory 
that  is  to  be  acceptable.  Any  theory  that  claims  to  account  for  new 
species  but  does  not  account  for  adaptations  is  at  best  only  a  partial 
explanation.  All  of  the  phenomena  which  have  been  briefly  men- 
tioned in  this  chapter,  together  with  the  more  intricate  phases  of 


THE  BACKGROUND  OF  DARWINISM— ADAPTATIONS         205 

general  adaptiveness  involved  in  the  idea  of  "  the  web  of  life/'  are  part 
of  the  background  of  Darwinism  and  were  in  the  mind  of  Darwin  when 
he  thought  out  the  great  generalization  called  "natural  selection." 
The  "web  of  Hfe"  idea  has  been  admirably  presented  by  Professor 
Thomson,  Scotland's  most  skilful  and  prolific  biological  writer.  The 
present  writer  feels  that  no  student  of  evolution  should  miss  the  oppor- 
tunity of  getting  into  the  spirit  of  Darwinism  with  this  distinguished 
author,  and  to  make  this  desideratum  easily  attainable,  the  chapter 
is  quoted  unchanged  as  part  of  the  general  text  and  immediately 
follows  this  discussion. 


CHAPTER  XV 

THE  BACKGROUND  OF  DARWINISM— Continued 

THE  WEB  OF  LIFE^ 

J.    ARTHUR   THOMSON 

Naturalists,  in  the  true  sense,  who  study  the  life  of  living  creatures 
in  nature,  have  always  been  distinguished  by  a  keen  perception  of  the 
interrelations  of  things.  Whether  we  take  Gilbert  White  as  repre- 
senting the  old  school,  or  W.  H.  Hudson  as  representing  the  new,  we 
get  from  their  observations  the  same  impression  of  nature  as  a  vibrat- 
ing system,  most  surely  and  subtly  interconnected.  But  it  seems 
just  to  say  that  no  naturalist,  before  or  since,  has  come  near  Darwin 
in  his  realisation  of  the  web  of  life,  in  his  clear  vision  and  picture  of  the 
vast  system  of  linkages  that  penetrates  throughout  the  animated 
world. 

Correlation  of  organisms  as  well  as  correlation  of  organs. — In 
thinking  of  a  living  body  we  are  accustomed  to  the  idea  of  the  cor- 
relation of  organs.  It  is  of  the  very  nature  of  an  organism  that  there 
should  be  mutual  dependence  among  its  parts.  The  organs  are  all 
partners  in  the  business  of  life,  and  if  one  member  changes  others  also 
are  affected.  This  is  especially  true  of  certain  organs  that  have 
developed  and  evolved  together,  and  are  knit  by  close  physiological 
bonds.  We  know  in  health  how  nerve  and  muscle,  brain,  and  sense 
organs,  heart  and  lungs,  are  closely  bound  together  in  the  bundle  of 
life.  We  know  in  disease  that  a  change  in  one  organ  often  affects 
another,  and  the  fact  remains  though  the  nexus  is  sometimes  myste- 
rious. The  state  of  our  liver  may  give  colour  to  our  whole  intellectual 
firmament,  and  a  slight  ocular  derangement  may  warp  a  wise  man's 
philosophy.  The  far-reaching  importance  of  a  little  organ  like  the 
thyroid  gland  beside  the  larynx  is  well  known;  our  intellectual  as  well 
as  our  bodily  health  depends  on  its  soundness.  Now,  just  as  there  is  a 
correlation  of  organs  within  the  body,  so  there  is  a  correlation  of 
organisms  in  that  system  of  things  which  we  call  Nature.  In  both 
cases  we  are  here  using  the  word  "  correlation  "  in  its  deeper  sense — 

^  From  J.  A.  Thomson,  Darwinism  and  Human  Life  (copyright  1909).  Used 
by  special  permission  of  the  publishers,  Henry  Holt  &  Company. 

206 


BACKGROUND  OF  DARWINISM— THE  WEB  OF  LIFE  207 

that  the  various  parts  are  more  than  mutually  dependent,  that  they 
are  in  some  measure  co-ordinated,  making  larger  systems  workable. 
What  the  metaphor  of  "the  web  of  Ufe"  suggests. — We  may  use 
the  metaphor  "web  of  life"  in  two  ways.  On  the  one  hand,  Nature 
has  a  woven  pattern  which  science  seeks  to  read,  each  science  following 
the  threads  of  a  particular  colour.  There  is  a  warp  and  woof  in  this 
web,  which  to  the  zoologist  usually  appear  as  "hunger"  and  "love." 
There  is  a  changing  pattern  in  the  web,  becoming  more  complex  as  the 
ages  pass;  and  this  is  evolution.  But  the  essential  idea  of  a  web  is  that 
of  interlinking  and  ramifying.  We  can  never  tell  where  a  thread  will 
lead  to.  If  one  be  pulled  out,  many  are  loosened.  This  is  true  of 
Nature  through  and  through. 

The  phrase  "web  of  life"  suggests  another  picture — the  web  of  a 
spider — often  an  intricate  system,  with  part  delicately  bound  to  part 
so  that  the  whole  system  is  made  one.  "The  quivering  fly  entangled 
in  a  corner  betrays  itself  throughout  the  web;  often  it  is  felt  rather 
than  seen  by  the  lurking  spinner.  So  in  the  substantial  fabric  of  the 
world  part  is  bound  to  part.  In  wind  and  weather,  or  in  the  business 
of  our  life,  we  are  daily  made  aware  of  results  whose  first  conditions  are 
very  remote;  and  chains  of  influence,  not  difficult  to  demonstrate, 
link  man  to  beast,  and  flower  to  insect.  The  more  we  know  of  our 
surroundings  the  more  we  realise  that  nature  is  a  vast  system  of  link- 
ages, that  isolation  is  impossible." 

Dependence  of  living  creatures  on  their  surroundings. — We  do 
not  know  what  life  in  principle  is,  but  we  may  describe  living  as  action 
and  reaction  between  organisms  and  their  environment.  This  is  the 
fundamental  relation — the  dependence  of  living  creatures  on  appro- 
priate surroundings,  and  the  primary  illustrations  of  linkages  must  be 
found  here.  The  living  creatures  are  real,  just  in  the  same  sense  as  the 
surroundings  are  real;  but  it  is  plain  that  we  cannot  abstract  the  living 
creatures  from  their  surroundings.  When  we  try  to  do  this  they  die — 
even  in  our  thought  of  them,  and  our  biology  is  only  necrology. 
Huxley  compared  a  living  creature  to  a  whirlpool  in  a  river;  it  is  always 
changing,  yet  always  apparently  the  same;  matter  and  energy  stream 
in  and  stream  out;  the  whirlpool  has  an  individuality  and  a  certain 
unity,  yet  it  is  wholly  dependent  upon  the  surrounding  currents.  One 
may  push  the  whirlpool  metaphor  too  far,  so  as  to  give  a  false  sim- 
plicity to  the  facts,  for  when  vital  whirlpools  began  to  be  there  also 
emerged  what  cannot  be  discerned  in  crystal  or  dewdrop — the  will  to 
live,  a  capacity  of  persistent  experience,  and  the  power  of  giving  rise  to 


2o8     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

other  lives.  To  ignore  this  is  to  attempt  a  falsely  simple  natural 
history.  But  what  Huxley's  metaphor  of  the  whirlpool  does  vividly 
express  is  the  dependence  of  living  creatures  on  their  surroundings. 
We  cannot  understand  either  the  whirlpool  or  the  trout  apart  from 
the  stream. 

When  we  think  out  this  fundamental  dependence  upon  surround- 
ings, we  see,  for  instance,  that  all  our  supplies  of  energy,  all  our  powers 
of  every  kind — with  our  own  hands,  or  by  the  use  of  animals,  or  by 
means  of  machinery — are  traceable  to  the  sun.  Or  again,  it  is  easy  to 
show  that  our  society  depends  fundamentally  not  on  gold,  but  on  iron. 
We  depend  for  food  on  plants  and  animals,  and  through  these  animals 
on  plants  ultimately;  the  plants  feed  upon  air,  water,  and  salts,  which, 
with  the  aid  of  the  energy  of  the  sunlight,  they  build  up  into  complex 
organic  compounds ;  they  cannot  do  this  unless  the  sun  shines  through 
a  screen  of  green  pigment  called  chlorophyll;  there  cannot  be  chloro- 
phyll without  iron;  therefore  our  whole  social  framework  is  founded 
on  iron. 

Nutritive  chains. — Plants  feed  on  their  inanimate  environment 
in  a  direct  way  that  is  impossible  to  animals,  so  we  pass  insensibly 
from  dependence  on  surroundings  to  those  nutritive  chains  which  bind 
living  creatures  together  in  long  series  often  quaintly  suggestive  of 
''The  House  That  Jack  Built"  and  similar  old  rhymes.  We  have 
ceased  to  wonder  at  the  circulation  of  the  blood  in  our  body;  have  we 
begun  to  wonder  enough  at  the  ceaseless  circulation  of  matter  in  the 
system  of  nature  ?  As  Heraclitus  said,  iravTa  pel,  all  things  are  in  flux. 
"The  rain  falls;  the  springs  are  fed;  the  streams  are  filled  and  flow  to 
the  sea;  the  mist  rises  from  the  deep  and  the  clouds  are  formed,  which 
break  again  on  the  mountain-side.  The  plant  captures  air,  water,  and 
salts,  and,  with  the  sun's  aid,  builds  them  up  by  vital  alchemy  into  the 
bread  of  life,  incorporating  this  into  itself.  The  animal  eats  the  plant 
and  a  new  incarnation  begins.  A II  flesh  is  grass.  The  animal  becomes 
part  of  another  animal,  and  the  reincarnation  continues."  The  silver 
cord  of  the  bundle  of  life  is  loosed,  and  earth  returns  to  earth.  The 
microbes  of  decay  break  down  the  dead,  and  there  is  a  return  to  air 
and  water  and  salts.  We  may  be  sure  that  nothing  real  is  ever  lost; 
we  are  sure  that  all  things  flow.  Penelope-like,  Nature  is  continually 
unravelling  her  web  and  making  a  fresh  start. 

Nexus  between  mud  and  clear  thinking. — To  keep  a  famous 
inland  fish-pond  from  giving  out,  some  boxes  of  mud  and  manure  were 
placed  at  the  sides.     Bacteria — the  minions  of  all  putrefaction — 


BACKGROUND  OF  DARWINISM— THE  WEB  OF  LIFE  209 

worked  in  the  mud  and  manure,  making  food  for  minute  Infusorians 
which  multiply  so  rapidly  that  there  may  be  a  million  from  one  in  a 
week's  time.  A  cataract  of  Infusorians  overflowed  from  box  to  pond, 
and  the  water-fleas  and  other  small  fry  gathered  at  the  foot  of  the  fall 
and  multiplied  exceedingly.  Thus  the  fishes  were  fed,  and,  as  fish- 
flesh  is  said  to  be  good  for  the  brain,  we  can  trace  a  nexus  from  mud  to 
clear  thinking.  What  was  in  the  mud  became  part  of  the  Infusoria  n, 
which  became  part  of  the  Crustacean,  which  became  part  of  the  fish, 
which  became  part  of  the  man.  And  it  is  thus  that  the  world  goes 
round. 

Correlation  between  catches  of  mackerel  and  amount  of  spring 
sunlight. — A  curious  and  most  interesting  correlation  has  been 
discovered  by  Dr.  E.  J.  Allen  between  catches  of  mackerel  and  the 
amount  of  sunlight.  The  more  sunshine  in  May,  the  more  mackerel 
at  Billingsgate.  How  does  this  work  out  ?  Mr.  G.  E.  Bullen  shows 
that  ''for  the  years  1903-1907  there  appears  to  be  a  correlation 
between  the  number  of  mackerel  taken  during  May,  and  the  amount 
of  Copepod  plankton,  upon  which  the  mackerel  feed,  taken  in  the 
neighborhood  of  the  fishing  grounds  during  the  same  month." 
Mr.  W.  J.  Dakin  shows  that  the  food  of  Copepods  consists  largely 
of  the  vegetable  organisms  of  the  plankton,  such  as  diatoms,  and  of 
Infusoria-like  organisms  called  Peridinidae.  But  the  production  of 
this  microscopic  plankton,  the  "stock"  of  the  "seasoup,"  depends 
partly  on  the  composition  of  the  sea-water,  partly  on  the  tempera- 
ture, and  partly  on  the  amount  of  light  available.  There  seems  to  be 
no  correlation  between  the  surface  temperature  and  the  abundance 
of  mackerel,  but  Dr.  Allen  has  shown  a  correspondence  between 
sunshine  and  the  catches.  Thus  we  see  that,  if  all  flesh  is  grass, 
then  in  the  same  sense  all  fish  is  diatom. 

Nutritive  chains  in  the  deep  sea. — If  we  pass  from  the  sunlit 
open  sea  to  the  floor  of  the  deep  sea — that  strange,  dark,  cold,  silent, 
plantless  world — we  find  carnivorous  animal  preying  upon  carnivorous 
animal  through  long  series — fish  feeds  on  fish,  fish  on  Crustacean, 
Crustacean  on  worm,  worm  on  still  smaller  fry,  and  all  ultimately 
depend  on  the  basal  food-supply — the  ceaseless  shower  of  moribund 
atomies  sinking  from  the  surface  waters  many  miles,  it  may  be,  over- 
head, like  the  snowflakes  on  a  quiet  winter  day. 

Dependence  of  one  organism  on  another  for  the  continuance  of 
the  species. — Passing  from  "nutritive  chains,"  we  may  select  a  few 
illustrations  of  the  dependence  of  one  creature  upon  another  for  the 


2IO      READINGS  IX   EVOLUTION,  GENETICS,  AND  EUGENICS 

continuance  of  its  kind.  The  crowning  instances  are  to  be  found  in  in- 
terrelations between  plants  and  animals  which  secure  cross-fertilisation 
and  the  distribution  of  seeds.  To  both  of  these  Darwin  devoted  much 
attention,  and  they  were  always  favourite  subjects  with  him. 

Everyone  knows  that  flowering  plants  and  flower-visiting  insects 
have  grown  up  throughout  long  ages  together,  in  alternate  influence 
and  mutual  perfecting.  They  are  now  fitted  to  one  another  as  hand 
to  glove.  The  insects  visit  the  flowers  for  food ;  in  so  doing  they  carry 
the  fertiUsing  golden  dust  from  blossom  to  blossom,  so  that  the 
possible  seeds  become  real  seeds. 

In  1793  a  Berlin  naturalist,  Christian  Konrad  Sprengel,  hke 
Darwin  in  his  perception  of  the  web  of  life,  published  a  pioneer  book 
entitled  The  Secret  of  Nature  Discovered  in  the  Structure  and  Fertili- 
zation of  Flowers,  in  which  he  showed  that  most  flowers  have 
nectar  which  insects  enjoy;  that  by  the  insects'  visits  polUnation  is 
secured;  that  there  is  no  detail  of  the  flower  without  its  meaning — 
the  colour  is  a  flag  to  attract  the  insect's  eye,  conspicuous  spots  are 
honey-guides  to  the  explorers,  there  are  arrangements  for  keeping  the 
pollen  dry  and  for  dusting  it  on  the  insects,  and  so  on.  If  Sprengel 
had  only  discovered  the  utility  of  the  cross-fertiHsation,  which  Darwin 
proved  experimentally,  his  work  could  hardly  have  been  overlooked 
for  nearly  seventy  years.  In  1841  it  came  into  Darwin's  hands,  and 
impressed  him  as  being  ''full  of  truth,"  although  ''with  some  little 
nonsense."     In  Darwin's  work  Sprengel  had  his  long-delayed  reward. 

Darwin's  instance  of  the  connection  between  cats  and  clover. — 
One  of  Darwin's  instances  of  the  web  of  life — given  in  connection  with 
the  pollination  of  flowers — has  become  familiar  all  over  the  world. 
It  should  never  become  trite  to  us  and  it  should  never  be  regarded  as 
more  than  a  particularly  clear  illustration  of  a  general  fact.  "  Plants 
and  animals,  remote  in  the  scale  of  nature,  are  bound  together  by  a 

web  of  complex  relations I  have  found,  from  experiments,  that 

humble-bees  are  almost  indispensable  to  the  fertilisation  of  the  heart' s- 
ease  {Viola  tricolor),  for  other  bees  do  not  visit  this  flower.  I  have  also 
found  that  the  visits  of  bees  are  necessary  for  the  fertilisation  of  some 
kinds  of  clover — thus,  100  heads  of  red  clover  {Trifolium  pratense) 
produced  27,000  seeds,  but  the  same  number  of  protected  heads  pro- 
duced not  a  single  seed.     Humble-bees  alone  visit  red  clover,  as  other 

bees  cannot  reach  the  nectar Hence  we  may  infer  as  highly 

probable  that,  if  the  whole  genus  of  humble-bees  became  extinct  or 
very  rare  in  England,  the  heart's-ease  and  red  clover  would  become 


BACKGROUND  OF  DARWINISM— THE  WEB  OF  LIFE 


211 


very  rare,  or  wholly  disappear."  We  know  that  the  red  clover 
imported  to  New  Zealand  did  not  bear  fertile  seeds  until  humble-bees 
were  also  imported.  "The  number  of  humble-bees  in  any  district 
depends  in  a  great  measure  on  the  number  of  field-mice,  which  destroy 
their  combs  and  nests;  and  Colonel  Newman,  who  has  long  attended 
to  the  habits  of  humble-bees,  believes  that  more  than  two-thirds  of 
them  are  thus  destroyed  all  over  England."  Now  the  number  of 
mice  is  largely  dependent,  as  everyone  knows,  on  the  number  of  cats; 
and  Colonel  Newman  says:  ''Near  villages  and  small  towns  I  have 
found  the  nests  of  humble-bees  more  numerous  than  elsewhere,  which  I 
attribute  to  the  number  of  cats  that  destroy  the  mice."  Thus  we  may 
say,  with  Darwin,  that  next  year's  crop  of  purple  clover  is  influenced 
by  the  number  of  humble-bees  in  the  district,  which  varies  with  the 
number  of  field-mice;    that  is  to  say,  with  the  abundance  of  cats! 

Scattering  of  seeds. — It  is  a  fascinating  chapter  of  natural  history 
which  tells  us  how  cross-pollination  is  effected — here  by  a  bee  and 
there  by  a  butterfly,  occasionally  by  a  long-billed  humming-bird 
beautifully  poised  before  the  flower  with  almost  invisibly  rapid  vibra- 
tions of  its  wings,  and  occasionally  by  a  slowly  moving  snail  of  epicure 
appetite.  But  not  less  important  is  the  part  played  by  animals  in  the 
scattering  of  seeds,  and  here  again  Darwin  gives  us  the  classic  case  of 
fourscore  seeds  germinating  out  of  a  ball  of  mud  from  a  bird's  foot. 
From  one  instance  you  may  learn  all,  and  see  that  much  of  Darwin's 
work  has  been  an  eloquent  commentary  on  that  memorable  saying 
about  the  sparrow  that  falls  to  the  ground.  Such  a  simple  event 
literally  sends  a  throb  through  surrounding  nature;  we  can  follow  its 
effects  a  few  steps,  just  as  we  follow  for  a  few  yards  the  ripples  made 
when  we  throw  a  stone  into  a  still  lake;  in  either  case  can  we  doubt 
that  the  spreading  influences  are  real,  though  they  pass  beyond 
our  ken? 

Interrelations  between  fresh-water  mussels  and  fishes. — As  a 
striking  illustration  of  the  inter-linking  of  different  forms  of  life,  we 
may  take  the  case  of  the  fresh-water  mussels  and  their  larvae.  The 
fertilised  eggs  develop  in  the  outer  gill-plate  of  the  mother-mussel,  and 
minute  bivalve  larvae,  called  Glochidia,  are  formed.  The  mussel  keeps 
these  within  the  cradle  until  a  fresh-water  fish — such  as  the  minnow — 
comes  into  the  vicinity,  and  then  she  sets  them  free.  In  a  way  that 
we  do  not  understand,  the  simple  constitution  of  the  larvae  is  tuned 
to  respond  to  the  presence  of  minnows  and  the  like,  and  with  snapping 
valves  they  manage  to  fix  themselves  to  their  host.     After  a  short 


212     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

period  of  temporary  parasitism,  at  the  end  of  which  there  is  a  meta- 
morphosis, they  drop  off  from  the  fish  into  the  mud,  often  far  from 
their  birth-place.  This  is  curious  enough,  but  the  idea  of  Unkages 
becomes  incandescent  in  the  mind  when  we  note  that,  just  as  the  fresh- 
water mussel  has  young  temporarily  parasitic  on  fishes,  so  a  fresh- 
water fish,  the  bitterUng  (Rhodeus  amarus),  has  its  young  temporarily 
parasitic  in  the  gills  of  the  mussel. 

Life-histories  of  parasites. — When  we  pass  to  parasites  in  a 
stricter  sense  we  find  the  most  extraordinary  interconnections,  the 
most  widely  separated  animals  often  sharing  a  parasite  between  them. 
Liver-rot,  which  has  repeatedly  killed  a  mil  Hon  sheep  in  a  year  in 
Britam  alone,  is  due  to  a  parasite  which  passes  from  sheep  to  water, 
from  water  to  water-snail,  from  water-snail  to  grass,  from  grass  to 
sheep.  The  tapeworm  of  the  cat  has  its  bladder-worm  stage  in  the 
mouse,  the  sturdie-worm  of  the  sheep's  bram  has  its  tape-worm  stage 
in  the  dog,  and  similar  relations  hold  for  hundreds  of  species.  The 
troublesome  threadworm  of  human  blood  {Filaria  sanguinis  hominis) 
is  transferred  from  man  to  man  by  the  mosquito,  and  the  guinea-worm 
which  was  probably  the  fiery  serpent  that  vexed  the  Israelites  in  the 
desert,  which  passes  into  man  in  drinking-water,  spends  its  youth 
in  a  minute  water-flea,  called  by  the  giant's  name  of  Cyclops.  The 
importance  cf  tse-tse  flies  in  transmitting  the  minute  animals  which 
cause  sleeping-sickness  and  allied  diseases  is  known  to  all.  We  have 
spoken  of  the  connection  between  cats  and  clover,  and  there  is  a  not 
less  striking  connection  between  cats  and  plague.  For  it  seems  to  have 
been  shown  in  India  that  the  more  cats  the  fewer  rats,  and  the  fewer 
rats  the  fewer  rat-fleas,  which  are  the  agents  in  passing  the  plague- 
germs  to  man. 

Far-reaching  influence  of  certain  animals;  earthworms. — We 
realise  the  idea  of  the  web  of  life  in  another  way  when  we  consider  the 
far-reaching  influence  of  particular  kinds  of  activity,  the  best  instance 
being  the  work  of  earthworms.  In  1777  Gilbert  White  got  at  the  very 
root  of  the  matter.  "The  most  insignificant  insects  and  reptiles  are  of 
much  more  consequence  and  have  more  influence  in  the  economy  of 

nature  than  the  incurious  are  aware  of Earthworms,  though  in 

appearance  a  small  and  despicable  link  in  the  chain  of  nature,  yet,  if 

lost,  would  make  a  lamentable  chasm Worms  seem  to  be  the 

great  promoters  of  vegetation,  which  would  proceed  but  lamely  with- 
out them,  by  boring,  perforating,  and  loosening  the  soil,  and  rendering 
it  pervious  to  rains  and  the  fibres  of  plants;   by  drawing  straws  and 


BACKGROUND  OF  DARWINISM— THE  WEB  OF  LIFE  213 

Stalks  of  leaves  and  twigs  into  it;  and,  most  of  all,  by  throwing  up  such 
infinite  numbers  of  lumps  of  earth  called  worm-casts,  which,  being 
their  excrement,  is  a  fine  manure  for  grain  and  grass.  Worms  prob- 
ably provide  new  soil  for  hills  and  slopes  where  the  rain  washes  the 
earth  away;  and  they  affect  slopes  probably  to  avoid  being  flooded. 
....  The  earth  without  worms  would  soon  become  cokl,  hard- 
bound, and  void  of  fermentation,  and  consequently   sterile 

These  hints  we  think  proper  to  throw  out,  in  order  to  set  the  inquisitive 
and  discerning  at  work.  A  good  monograph  of  worms  would  afford 
much  entertainment  and  information  at  the  same  time,  and  would 
open  a  large  and  new  field  in  natural  history." 

The  monograph  that  Gilbert  White  wished  for  in  1777  was  pub- 
lished by  Darwin  in  i88r,  the  year  before  he  died — ''  the  completion," 
he  said,  "of  a  short  paper  read  before  the  Geological  Society  more  than 
forty  years  ago."  With  his  characteristic  thoroughness  and  patience 
he  worked  out  the  part  that  earthworms  have  played  in  the  history 
of  the  earth,  and  proved  that  they  deserve  to  be  called  the  most  useful 
animals.  By  their  burrowing  they  loosen  the  earth,  making  way  for 
the  plant  rootlets  and  the  raindrops;  by  bruising  the  soil  in  their 
gizzards,  they  reduce  the  particles  to  more  useful,  powdery  form;  by 
burying  the  surface  with  castings  brought  up  from  beneath,  they  have 
been  for  untold  ages  ploughers  before  the  plough,  and  by  burying  leaves 
they  have  made  a  great  part  of  the  vegetable  mould  over  the  whole 
earth.  In  illustration  of  the  last  point,  we  may  notice  that  we  recently 
found  thirteen  midribs  of  the  leaves  of  the  rowan,  or  mountain  ash, 
radiating  round  one  hole  like  the  spokes  of  a  wheel;  the  withering 
leaflets  had  been  carried  down,  and  two  were  sticking  up  at  the  mouth 
of  the  burrow;  that  meant  91  leaflets  to  one  hole.  Darwin  showed 
that  there  often  are  50,000  (and  there  may  be  500,000)  earthworms 
in  an  acre;  that  they  often  pass  ten  tons  of  soil  per  acre  per  annum 
through  their  bodies;  and  that  they  often  cover  the  surface  at  the  rate 
of  three  inches  in  fifteen  years.  Though  our  British  worms  only  pass 
out  about  20  oz.  of  earth  in  a  year,  the  weights  thrown  up  in  a  year  on 
two  separate  square  yards  which  Darwin  watched  were  respectively 
6  .75  lb.  and  8  .387  lb.,  which  correspond  to  14^  and  18  tons  per  acre 
per  annum. 

We  follow  the  work  further  and  it  becomes  evident  that  the  con- 
stant exposure  of  the  soil  bacteria  on  the  surface  is  bound  to  be 
important,  on  the  one  hand,  in  allowing  them  to  be  scattered  by  wind 
and  rain  on  the  other  in  exposing  them  to  the  beneficent  action  of  the 


214     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

sunlight — which  is  the  most  universal,  effective,  and  economical  of  all 
germicides. 

In  Yorubaland,  on  the  West  Coast  of  Africa,  Mr.  Alvan  Millson 
calculated  that  about  62,233  tons  of  subsoil  are  brought  every  year 
to  the  surface  of  each  square  mile,  and  that  every  particle  of  earth,  to 
the  depth  of  two  feet,  is  brought  to  the  surface  once  in  twenty-seven 
years.     It  need  hardly  be  added  that  the  district  is  fertile  and  healthy. 

Earthworms  play  their  part  in  the  disintegration  of  rocks,  letting 
the  solvent  humus-acids  of  the  soil  down  to  the  buried  surface.  Their 
castings  on  the  hill-slopes  are  carried  down  by  wind  and  rain  and  go 
to  swell  the  alluvium  of  the  distant  valleys  or  the  wasted  treasures  of 
the  sea.  The  well-known  parallel  ledges  along  the  slopes  of  grass-clad 
hills  are  partly  due  to  earthworm  castings  caught  on  sheep- tracks,  and 
thus  we  begin  to  connect  the  earthworms  not  only  with  our  wheat- 
supply  but  wdth  our  scenery.  Well  may  we  say,  with  Darwin:  ''It 
may  be  doubted  whether  there  are  many  other  animals  which  have 
played  so  important  a  part  in  the  history  of  the  world  as  have  these 
lowly  organised  creatures."  Those  who  wish  to  understand  Darwin- 
ism should  always  begin  with  Darwin's  last  book — The  Formation 
of  Vegetable  Mould  through  the  Action  of  Worms  (1881).  It  illus- 
trates the  web  of  life,  the  idea  of  which  is  essential  to  an  understanding 
of  the  struggle  for  existence  and  natural  selection.  But  it  also  illus- 
trates what  Darwin  had  learned  from  Lyell — that  great  results  may 
be  brought  about  by  accumulation  of  infinitesimal  items.  As  Professor 
A.  Milnes  Marshall  said:  "The  lesson  to  be  derived  from  Darwin's 
life  and  work  cannot  be  better  expressed  than  as  the  cumulative  im- 
portance of  infinitely  little  things.  ^^ 

Termites,  or  white  ants. — Henry  Drummond,  in  his  Tropical 
Africa,  tried  to  make  out  a  case  for  the  agricultural  importance  of 
termites,  or  white  ants.  It  is  well  known  that  these  old-fashioned 
insects  have  a  pruning  action  in  the  forest,  destroying  dead  wood  with 
great  rapidity.  Houses  and  furniture,  fences  and  boxes,  as  well  as 
forest- trees,  fall  under  their  jaws.  In  some  places,  "if  a  man  lay 
down  to  sleep  with  a  wooden  leg,  it  would  be  a  heap  of  sawdust  in  the 
morning."  But  what  of  the  termites'  agricultural  importance  ?  The 
point  is  that  they  keep  the  soil  circulating  by  constructing  earthen 
tunnels  up  the  sides  of  trees  and  posts  and  by  making  huge  obelisk-like 
ant-hills,  or  termitaries.  "The  earth-tubes  crumble  to  dust,  which  is 
scattered  by  the  wind;  the  rams  lash  the  forests  and  soils  with  fury, 
and  wash  off  the  loosened  grains  to  swell  the  alluvium  of  a  distant 


BACKGROUND  OF  DARWINISM— THE  WEB  OF  LIFE  215 

valley."  It  must  be  noted,  however,  that  Drummond  did  not  prove 
his  case  with  sufficient  precision,  and  there  is,  as  Eschcrich  points  out 
in  his  beautiful  study  of  termites,  this  difficulty,  that,  while  the  cast- 
ings of  earthworms  are  soft  and  loose,  the  earth-tubes  and  construc- 
tions of  termites  are  stony. 

Escherich  does,  however,  admit  that  the  termites  have  some 
agricultural  importance,  and  he  points  out  that  there  are  other  serv- 
ices to  be  put  to  the  credit  side  of  their  account.  They  prune  off 
wood  that  has  begun  to  go;  they  destroy  rotting  things,  including  the 
bodies  of  small  animals;  they  make  for  cleanliness  and  health.  In 
some  low-lying  tracts,  as  Silvestri  has  shown,  there  are  dry  stretches, 
"termite  islands,"  which  have  been  gradually  built  up  from  the 
broken-down  remains  of  termitaries.  Nor  should  it  be  forgotten  that 
the  white  ants  are  often  used  as  food.  On  the  other  hand,  Escherich 
does  not  hesitate  to  rank  them  as  among  the  great  hindrances  to  the 
spread  of  civilisation.  They  insidiously  devour  everything  wooden, 
from  the  telegraph-post  to  the  wooden  butt  of  the  gun  hanging  against 
the  wall,  from  books  in  the  library  to  corks  in  the  cellar.  There  does 
not  seem  sufficiently  precise  information  in  regard  to  the  living  plants 
that  they  attack,  and  no  safe  general  statement  can  be  made  except 
that  their  appetite  is  large  and  catholic. 

With  a  centre  in  earthworms,  what  a  variety  of  interests  must  be 
included  within  the  radius  of  their  life  and  work! — centipedes,  birds, 
moles,  seedlings,  man.  The  same  is  true  of  termites,  and  two  further 
illustrations  may  be  given.  Observers  have  reported  about  thirty 
different  species  of  termites  with  the  habit  of  feeding  on  fungi  gro\\Ti 
within  the  termitary  on  specially  constructed  mazy  beds.  The  habit 
is  interesting  in  many  ways;  for  instance,  because  the  fungi  afford 
a  supply  of  nitrogenous  material  which  is  scarce  in  the  ordinary  diet 
of  wood,  and  also  because  a  similar  habit  occurs  in  the  quite  unrelated 
true  ants.  Finally,  the  web  is  illustrated  by  the  numerous  boarders, 
mostly  beetles,  that  are  found  in  the  termitaries — not  hostile  intruders 
or  parasites,  but  guests  which  are  fed  and  cared  for  apparently  for  the 
sake  of  a  palatable  exudation  with  a  pleasant,  narcotising  effect  on  the 
termites.  With  a  centre  in  termites,  what  a  variety  of  interests  must 
we  not  include  within  the  radius  of  their  hfe  and  work  I — fungi  and 
trees,  beetles  and  birds,  lizards  and  anteaters,  and  man  more  than  any. 

The  hand  of  life  upon  the  earth.— The  hand  of  life  has  been 
working  upon  the  earth  for  untold  ages.  T^ke  plants,  for  instance. 
The  seaweeds  lessen  the  force  of  the  waves,  the  lichens  eat  into  the 


2l6      READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

rocks,  the  mosses  form  huge  sponges  on  the  moors  which  keep  the 
streams  flowing  in  days  of  drought.  Many  Httle  plants  are  forever 
smoothing  away  the  wrinkleson  the  earth's — their  mother's — face,  and 
they  adorn  her  with  jewels.  Others  that  have  formed  coal  have  enriched 
her  with  ages  of  entrapped  sunlight.  The  grass — which  began  to 
appear  in  Tertiary  ages — ^protects  the  earth  like  a  garment;  the 
forests  affect  rainfall  and  temper  climate,  besides  sheltering  multitudes 
of  living  things,  to  many  of  whom  every  blow  of  the  axe  is  a  death- 
knell.  No  plant,  from  bacterium  to  oak-tree,  lives  or  dies  to  itself, 
or  is  without  its  influence  upon  the  earth.  So  among  animals  there 
are  destructive  borers  and  burrowers  and  conservative  agents,  such 
as  the  coral-polyps  and  the  chalk-forming  Foraminifera. 

Practical  importance  of  a  realisation  of  the  web  of  life. — What 
has  Darwinism  to  do  with  human  Hfe  ?  The  answer  at  this  stage  in 
our  inquiry  is  clear:  we  must  respect  the  web  of  life  if  we  wish  to 
master  Nature.  She  must  be  humoured,  not  bullied.  Emerson 
included  in  his  vision  of  a  perfected  earth  the  absence  of  spiders,  but 
the  absence  of  spiders — which  snare  so  many  injurious  insects — would 
mean  the  absence  of  much  else,  man  probably  included.  In  a  northern 
county  in  Scotland  the  proprietors  were  justly  annoyed  at  the  injuries 
inflicted  on  young  trees  by  squirrels,  and  they  formed  a  squirrel  club, 
setting  a  price  on  the  beautiful  rodent's  head.  Perhaps  a  wiser  course 
would  have  been  to  begin  by  inquiring  what  disturbance  of  the  balance 
of  nature  had  allowed  the  squirrels  to  multiply  so  disastrously.  But, 
after  a  period  of  squirrel-slaughter  and  some  jubilation  thereat,  a 
cloud  began  to  rise  in  the  sky.  The  wood-pigeons  were  multiplying 
worse  than  ever,  and  the  farmers,  at  least,  said  with  no  uncertain  voice 
that  they  preferred  the  squirrels.  An  imperfect  recognition  of  the 
web  of  life  had  left  out  of  account  the  notable  fact  that  squirrels 
destroy  large  numbers  of  young  wood-pigeons. 

One  of  the  hopeful  symptoms  of  the  last  few  years  is  the  reawaken- 
ing of  an  interest  in  woods  and  forests.  Everyone  knows  how  terribly 
these  have  been  wasted,  and  how  the  disastrous  results  have  affected 
rainfall  and  irrigation,  climate  and  crops,  and  even  the  character  of  the 
people.  Here  what  was  once  a  pleasant  stream  is  now  like  a  gravelly 
road,  and  there  the  fertile  plains  are  flooded;  here  the  wind  is  sweeping 
away  the  soil,  and  there  both  beauty  and  health  have  departed.  The 
birds  which  the  woods  once  sheltered  are  driven  elsewhere,  and  the 
insect-pests  are  rife  among  the  crops.  For  ''the  cheapest  and  most 
effective  insecticides  are  birds." 


BACKGROUND  OF  DARWINISM— THE  WEB  OF  LIFE  217 

The  recognition  of  consequences — often  far-reaching — grows  with 
us  as  we  work  with  the  idea  of  the  web  of  hfe,  as  we  see  in  proper 
perspective  the  criminahty  of  those  who  are  ruthless.  President 
Roosevelt  has  declared  his  abomination  of  "the  land-skinner" — ''the 
individual  whose  idea  of  developing  the  country  is  to  cut  every  stick 
of  timber  off  it,  and  then  leave  a  barren  desert  for  the  home-maker 
who  comes  in  after  him.  That  man  is  a  curse,  and  not  a  blessing  to  the 
country.  The  prop  of  the  country  must  be  the  man  who  intends  so 
to  run  his  business  that  it  will  be  profitable  to  his  children  after  him." 
Every  right-thinking  man,  and  especially  those  who  have  grasped  the 
idea  of  the  web  of  life,  will  say  with  Roosevelt,  "I  am  against  the  land- 
skinner  every  time." 

It  may  be  said  that  man  must  exterminate  a  good  deal  if  he  is  to 
go  on  peaceably  with  his  business,  and  it  will  be  admitted  that  there 
has  never  been  a  strong  enthusiasm,  humanitarian  or  otherwise, 
against  the  elimination  of  rattlesnakes,  and  such  like.  The  natural- 
ist's answer  is  that  every  crusade  should  be  carefully  considered  on  its 
own  merits,  and  that  every  careless  and  hasty  destruction  of  life  is  to  be 
condemned.  Even  in  regard  to  snakes  killing  may  be  carried  too  far. 
Some  creatures  are,  as  it  were,  on  the  fringes  of  the  web,  while  others 
occupy  a  position  where  many  threads  meet.  It  is  scientifically  and 
aesthetically  deplorable  that  birds  like  the  great  auk  and  mammals 
like  the  quagga  should  have  been  exterminated,  but  it  is  practically 
much  more  deplorable  that  we  have  lost  so  many  hawks  and  weasels 
and  other  members  of  that  pertinacious  army  whose  guerilla  warfare 
keeps  hundreds  of  more  humdrum  creatures  up  to  the  scratch,  and 
keeps  "vermin"  from  becoming  a  plague.  Moreover,  it  is  extremely 
difficult  to  tell  what  may  be  the  consequences  of  exterminating  any 
creature — remote  as  it  may  seem  from  the  beaten  track  of  human 
affairs.  One  of  the  obvious  lessons  of  Darwinism  is  that  we  should  be 
slow  to  call  any  change  unimportant.  Everything  counts,  or  may 
count.  A  so-called  unimportant  animal  is  destroyed  and  no  imme- 
diate ill  effects  are  seen.     But  who  can  tell  ? 

Very  pertinent,  for  instance,  is  the  question:  What  about  the 
parasites  that  used  to  complete  their  life-history  in  romantic  routine 
in  this  extinguished  animal  ?  Have  we  extinguished  the  parasite  also  ? 
Or  is  it  waiting,  with  a  whip  of  scorpions,  to  chastise  mankind  for 
their  ignorance  of  Darwinism  ? 

The  practical  importance  of  recognising  the  web  of  life  has  been 
proved  by  the  heavy  penalties  which  man  has  often  had  to  pay  for 


2i8      READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

disturbing  the  balance  of  nature,  careless  of  results  and  ruthless  of 
beauty,  for  not  admitting  that  if  we  would  master  Nature  we  must 
first  understand  her.  How  much  has  Australia  had  to  pay  for  the 
introduction  of  rabbits  in  i860,  or  America  for  sparrows  ?  Sometimes 
the  introduction  has  been  unconscious,  and  man  has  only  to  blame 
himself  for  letting  the  intruder  take  hold,  as  in  the  case  of  the  Phyl- 
loxera in  France,  or  of  the  Colorado  Beetle  in  Ireland.  "Ignorance 
of  nature,"  Mr.  A.  H.  S.  Lucas  says,  "is  costly.  By  disturbing  the 
balance  of  nature,  man  has  introduced  foes  into  his  own  household." 
Speaking  of  Australia,  he  says:  "How  much  is  needed  for  the  eradi- 
cation of  Bathurst  Burr,  Prickly  Pear,  Water-hyacinth,  Bramble  and 
Sweetbriar,  Codlin  Moth,  Waxy  Scale,  Pear  Slug,  and  Red  Spider, 
owing  to  carelessness  or  lack  of  knowledge  in  early  days?" 

An  obvious  moral  is  that  we  should  be  careful  in  our  introduc- 
tions of  new  organisms — -man  included — 'into  new  surroundings.  The 
primary  consequences  may  be  predictable,  but  the  secondary  and  the 
tertiary  consequences — who  is  sufficient  for  these  things  ?  We  have 
records  of  the  unconscious  introduction  of  rats  into  Jamaica,  where 
they  became  a  pest.  To  destroy  them  mongooses  were  imported,  and 
the  rats  were  soon  checked.  But  the  m^ongooses,  having  finished  the 
rats,  began  to  eat  up  the  poultry  and  young  birds  of  various  kinds. 
As  this  went  on  the  injurious  insects  and  ticks,  that  the  birds  used  to 
eat,  began  to  gain  the  ascendant.  A  recent  report — which  requires 
confirmation — says  that  the  increase  of  ticks  is  making  life  a  burden 
to  the  mongooses.  Thus  a  balance  will  be  again  arrived  at.  There 
is  no  doubt  of  that,  but  how  much  is  often  unnecessarily  lost  by  the 
way! 


CHAPTER  XVI 
NATURAL  SELECTION 

CHARLES   DARWIN 

Introductory  Note. — This  entire  chapter  is  made  up  of  carefully  chosen 
passages  from  Darwin's  Origin  of  Species.  So  much  has  falsely  been  callerl 
"Darwinism"  that  it  is  well  for  the  reader  to  have  a  statement  of  Darwin's  views 
in  his  own  words.  Every  student  of  evokition  should  read  the  whole  of  the  Origin 
of  Species.  It  is  all  so  good  that  one  finds  it  diflticult  to  leave  out  anything.  The 
following  excerpts  will,  we  believe,  give  the  gist  of  natural  selection. 

We  present  first  certain  of  the  ideas  that  underlie  or  are  postulates  of  the 
theory;  then  the  theory  itself  is  presented;  the  theory  of  sexual  selection  inter- 
polated; and  then  follow  examples  of  the  way  in  which  adaptations  are  accounted 
for  by  natural  selection.  Darwin's  own  statement  of  the  most  serious  difficulties 
and  objections  to  the  theory,  and  his  answers  to  these,  bring  this  chapter  to  a  close. 

FOUNDATION  STONES  OF  NATURAL  SELECTION 
darwin's  own  estimate  as  to  the  role  of  natural  selection  in  evolution 
No  one  ought  to  feel  surprised  at  much  remaining  as  yet  unex- 
plained in  regard  to  the  origin  of  species  and  varieties,  if  he  make  due 
allowance  for  our  profound  ignorance  in  regard  to  the  mutual  relations 
of  the  many  beings  which  live  around  us.  Who  can  explain  why  one 
species  ranges  widely  and  is  very  numerous,  and  why  another  aUied 
species  has  a  narrow  range  and  is  rare  ?  Yet  these  relations  are  of  the 
highest  importance,  for  they  determine  the  present  welfare  and,  as  I 
believe,  the  future  success  and  modification  of  every  inhabitant  of  this 
world.  Still  less  do  we  know  of  the  mutual  relations  of  the  innumer- 
able inhabitants  of  the  world  during  the  many  past  geological  epochs 
in  its  history.  Although  much  remains  obscure,  and  will  long  remain 
obscure,  I  can  entertain  no  doubt,  after  the  most  deliberate  study 
and  dispassionate  judgment  of  which  I  am  capable,  that  the  view 
which  most  naturalists  until  recently  entertained,  and  which  I  for- 
merly entertained — namely,  that  each  species  has  been  independently 
created — is  erroneous.  I  am  fully  convinced  that  species  are  not 
immutable;  but  that  those  belonging  to  what  are  called  the  same 
genera  are  lineal  descendants  of  some  other  and  generally  extinct 
species,  in  the  same  manner  as  the  acknowledged  varieties  of  any  one 
species  are  the  descendants  of  that  species.  Furthermore,  I  am  con- 
vinced that  Natural  Selection  has  been  the  most  important,  l)ut  not 
the  exclusive,  means  of  modification. 

219 


2  20     RE.\DINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

effects  of  habit  and  of  the  use  or  disuse  of  parts;   correlated 

variation;  inheritance 

Changed  habits  produce  an  inherited  effect,  as  in  the  period  of  the 
flowering  of  plants  when  transported  from  one  cHmate  to  another. 
With  animals  the  increased  use  or  disuse  of  parts  has  had  a  more 
marked  influence;  thus  I  find  in  the  domestic  duck  that  the  bones  of 
the  wing  weigh  less  and  the  bones  of  the  leg  more,  in  proportion  to  the 
whole  skeleton,  than  do  the  same  bones  in  the  wild-duck;  and  this 
change  may  be  safely  attributed  to  the  domestic  duck  flying  much 
less,  and  walking  more,  than  its  wild  parents.  The  great  and  inherited 
development  of  the  udders  in  cows  and  goats  in  countries  where 
they  are  habitually  milked,  in  comparison  with  these  organs  in  other 
countries,  is  probably  another  instance  of  the  effects  of  use.  Not 
one  of  our  domestic  animals  can  be  named  which  has  not  in  some 
country  drooping  ears;  and  the  view,  which  has  been  suggested  that 
the  drooping  is  due  to  disuse  of  the  muscles  of  the  ear,  from  the 
animals  being  seldom  much  alarmed,  seems  probable. 

Many  laws  regulate  variation,  some  few  of  which  can  be  dimly 
seen,  and  will  hereafter  be  briefly  discussed.  I  will  here  only  allude 
to  what  may  be  called  correlated  variation.  Important  changes  in  the 
embryo  or  larva  will  probably  entail  changes  in  the  mature  animal. 
In  monstrosities,  the  correlations  between  quite  distinct  parts  are 
very  curious;  and  many  instances  are  given  in  Isidore  Geoffroy  St. 
Hilaire's  great  work  on  this  subject.  Breeders  believe  that  long  limbs 
are  almost  always  accompanied  by  an  elongated  head.  Some  instances 
of  correlation  are  quite  whimsical:  thus  cats  which  are  entirely  white 
and  have  blue  eyes  are  generally  deaf;  but  it  has  been  lately  stated  by 
Mr.  Tait  that  this  is  confined  to  the  males.  Color  and  constitutional 
peculiarities  go  together,  of  which  many  remarkable  cases  could  be 
given  amongst  animals  and  plants.  From  facts  collected  by  Heu- 
singer,  it  appears  that  white  sheep  and  pigs  are  injured  by  certain 
plants,  whilst  dark-colored  individuals  escape:  Professor  Wyman  has 
recently  communicated  to  me  a  good  illustration  of  this  fact;  on  ask- 
ing some  farmers  in  Virginia  how  it  was  that  all  their  pigs  were  black, 
they  informed  him  that  the  pigs  ate  the  paint-root  (Lachnanthes) , 
which  colored  their  bones  pink,  and  which  caused  the  hoofs  of  all  but 
the  black  varieties  to  drop  off;  and  one  of  the"  crackers"  (i.e., Virginia 
squatters)  added,  ''we  select  the  black  members  of  a  litter  for  raising, 
as  they  alone  have  a  good  chance  of  living."  Hairless  dogs  have 
imperfect  teeth;    long-haired  and  coarse-haired  animals  are  apt  to 


NATURAL  SELECTION  221 

have,  as  is  asserted,  long  or  many  horns;  pigeons  with  feathered  feet 
have  skin  between  their  outer  toes;  pigeons  with  short  beaks  have 
small  feet,  and  those  with  long  beaks  large  feet.  Hence  if  man  goes 
on  selecting,  and  thus  augmenting,  any  peculiarity,  he  will  almost 
certainly  modify  unintentionally  other  parts  of  the  structure,  owing 
to  the  mysterious  laws  of  correlation. 

darwin's  idea  of  the  causes  responsible  for  the  origin  of  domestic  races 

To  sum  up  on  the  origin  of  our  domestic  races  of  animals  and 
plants.  Changed  conditions  of  life  are  of  the  highest  importance  in 
causing  variability,  both  by  acting  directly  on  the  organization,  and 
indirectly  by  affecting  the  reproductive  system.  It  is  not  probable 
that  variability  is  an  inherent  and  necessary  contingent,  under  all 
circumstances.  The  greater  or  less  force  of  inheritance  and  reversion 
determine  whether  variations  shall  endure.  Variability  is  governed  by 
many  unknown  laws,  of  which  correlated  growth  is  probably  the  most 
important.  Something,  but  how  much  we  do  not  know,  may  be 
attributed  to  the  definite  action  of  the  conditions  of  life.  Some,  per- 
haps a  great,  effect  may  be  attributed  to  the  increased  use  or  disuse 
of  parts.  The  final  result  is  thus  rendered  infinitely  complex.  In 
some  cases  the  intercrossing  of  aboriginally  distinct  species  appears  to 
have  played  an  important  part  in  the  origin  of  our  breeds.  When 
several  breeds  have  once  been  formed  in  any  country,  their  occasional 
intercrossing,  with  the  aid  of  selection,  has,  no  doubt,  largely  aided  in 
the  formation  of  new  sub-breeds;  but  the  importance  of  crossing  has 
been  much  exaggerated,  both  in  regard  to  animals  and  to  those  plants 
which  are  propagated  by  seed.  With  plants  which  are  temporarily 
propagated  by  cuttings,  buds,  etc.,  the  importance  of  crossing  is 
immense;  for  the  cultivator  may  here  disregard  the  extreme  variability 
both  of  hybrids  and  of  mongrels,  and  the  sterility  of  hybrids;  but 
plants  not  propagated  by  seed  are  of  little  importance  to  us,  for  their 
endurance  is  only  temporary.  Over  all  these  causes  of  Change,  the 
accumulative  action  of  Selection,  whether  apphed  methodically  and 
quickly,  or  unconsciously  and  slowly  but  more  efficiently,  seems  to 
have  been  the  predominant  Power. 

darwin's  idea  of  the  origin  of  varieties,  species,  and  genera  in  nature 
Finally,  varieties  cannot  be  distinguished  from  species — except, 
first,  by  the  discovery  of  intermediate  linking  forms;   and,  secondly, 
by  a  certain  indefinite  amount  of  difference  between  them;   for  two 


222      READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

forms,  if  differing  very  little,  are  generally  ranked  as  varieties,  not- 
withstanding that  they  cannot  be  closely  connected;  but  the  amount 
of  difference  considered  necessary  to  give  to  any  two  forms  the  rank 
of  species  cannot  be  defined.  In  genera  having  more  than  the  average 
number  of  species  in  any  country,  the  species  of  these  genera  have 
more  than  the  average  number  of  varieties.  In  large  genera  the  species 
are  apt  to  be  closely,  but  unequally,  allied  together,  forming  little 
clusters  round  other  species.  Species  very  closely  allied  to  other 
species  apparently  have  restricted  ranges.  In  all  these  respects  the 
species  of  large  genera  present  a  strong  analogy  with  varieties.  And 
we  can  clearly  understand  these  analogies,  if  species  once  existed  as 
varieties,  and  thus  originated;  whereas,  these  analogies  are  utterly 
inexplicable  if  species  are  independent  creations. 

We  have,  also,  seen  that  it  is  the  most  flourishing  or  dominant 
species  of  the  larger  genera  within  each  class  which  on  an  average  yield 
the  greatest  number  of  varieties;  and  varieties,  as  we  shall  hereafter 
see,  tend  to  become  converted  into  new  and  distinct  species.  Thus 
the  larger  genera  tend  to  become  larger;  and  throughout  nature  the 
forms  of  life  which  are  now  dominant  tend  to  become  still  more  domi- 
nant by  leaving  many  modified  and  dominant  descendants.  But  by 
steps  hereafter  to  be  explained,  the  larger  genera  also  tend  to  break  up 
into  smaller  genera.  And  thus,  the  forms  of  life  throughout  the  uni- 
verse become  divided  into  groups  subordinate  to  groups. 

THE  TERM  "struggle  FOR  EXISTENCE"  USED  IN  A  LARGE  SENSE 

I  should  premise  that  I  use  this  term  in  a  large  and  metaphorical 
sense  including  dependence  of  one  being  on  another,  and  including 
(which  is  more  important)  not  only  the  life  of  the  individual,  but 
success  in  leaving  progeny.  Two  canine  animals,  in  a  time  of  dearth, 
may  be  truly  said  to  struggle  with  each  other  which  shall  get  food  and 
live.  But  a  plant  on  the  edge  of  a  desert  is  said  to  struggle  for  life 
against  the  drought,  though  more  properly  it  should  be  said  to  be 
dependent  on  the  moisture.  A  plant  which  annually  produces  a 
thousand  seeds,  of  which  only  one  of  an  average  comes  to  maturity, 
may  be  more  truly  said  to  struggle  with  the  plants  of  the  same 
and  other  kinds  which  already  clothe  the  ground.  The  mistletoe  is 
dependent  on  the  apple  and  a  few  other  trees,  but  can  only  in  a 
far-fetched  sense  be  said  to  struggle  with  these  trees,  for,  if  too  many 
of  these  parasites  grow  on  the  same  tree,  it  languishes  and  dies.  But 
several  seedling  mistletoes,  growing  close  together  on  the  same  branch, 


NATURAL  SELECTION 


223 


may  more  truly  be  said  to  struggle  with  each  other.  As  the  mistletoe 
is  disseminated  by  birds,  its  existence  depends  on  them;  and  it  may 
metaphorically  be  said  to  struggle  with  other  fruit-bearing  i)lants, 
in  tempting  the  birds  to  devour  and  thus  disseminate  its  seeds.  In 
these  several  senses,  which  pass  into  each  other,  I  use  for  con\en- 
ience'  sake  the  general  term  of  Struggle  for  Existence. 

GEOMETRICAL  RATIO  OF  INCREASE 

A  struggle  for  existence  inevitably  follows  from  the  high  rate  at 
which  all  organic  beings  tend  to  increase.  Every  being,  which  during 
its  natural  lifetime  produces  several  eggs  or  seeds,  must  suffer  destruc- 
tion during  some  period  of  its  life,  and  during  some  season  or  occasional 
year,  otherwise,  on  the  principle  of  geometrical  increase,  its  numbers 
would  quickly  become  so  inordinately  great  that  no  country  could 
support  the  product.  Hence,  as  more  individuals  are  produced  than 
can  possibly  survive,  there  must  in  every  case  be  a  struggle  for  exist- 
ence, either  one  individual  with  another  of  the  same  species,  or  with 
the  individuals  of  distinct  species,  or  with  the  physical  conditions  of 
life.  It  is  the  doctrine  of  Malthus  applied  with  manifold  force  to 
the  whole  animal  and  vegetable  kingdoms;  for  in  this  case  there  can 
be  no  artificial  increase  of  food,  and  no  prudential  restraint  from 
marriage.  Although  some  species  may  be  now  increasing,  more  or 
less  rapidly,  in  numbers,  all  cannot  do  so,  for  the  world  would  not 
hold  them. 

NATURAL   selection;    OR   THE    SURVIVAL   OF   THE   FITTEST 

How  will  the  struggle  for  existence,  briefly  discussed  in  the  last 
chapter,  act  in  regard  to  variation  ?  Can  the  principle  of  selection, 
which  we  have  seen  is  so  potent  in  the  hands  of  man,  appl}'  under 
nature  ?  I  think  we  shall  see  that  it  can  act  most  efficiently.  Let  the 
endless  number  of  slight  variations  and  individual  differences  occurring 
in  our  domestic  productions,  and,  in  a  lesser  degree,  in  those  under 
nature,  be  borne  in  mind;  as  well  as  the  strength  of  the  hereditary 
tendency.  Under  domestication,  it  may  be  truly  said  that  the  whole 
organization  becomes  in  some  degree  plastic.  But  the  variability, 
which  we  almost  universally  meet  w^ith  in  our  domestic  productions, 
is  not  directly  produced,  as  Hooker  and  Asa  Gray  have  well  remarked, 
by  man;  he  can  neither  originate  varieties,  nor  prevent  their  occur- 
rence; he  can  only  preserve  and  accumulate  such  as  do  occur.  Unin- 
tentionally he  exposes  organic  beings  to  new  and  changing  conditions 


224     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

of  life,  and  variability  ensues;  but  similar  changes  of  conditions  might 
and  do  occur  under  nature.  Let  it  also  be  borne  in  mind  how  infinitely 
complex  and  close-fitting  are  the  mutual  relations  of  all  organic  beings 
to  each  other  and  to  their  physical  conditions  of  life;  and  consequently 
what  infinitely  varied  diversities  of  structure  might  be  of  use  to 
each  being  under  changing  conditions  of  life.  Can  it,  then,  be 
thought  improbable,  seeing  that  variations  useful  to  man  have 
undoubtedly  occurred,  that  other  variations  useful  in  some  way  to 
each  being  in  the  great  and  complex  battle  of  life,  should  occur  in 
the  course  of  many  successive  generations  ?  If  such  do  occur,  can 
we  doubt  (remembering  that  many  more  individuals  are  born  than 
can  possibly  survive)  that  individuals  having  any  advantage,  however 
slight,  over  others,  would  have  the  best  chance  of  surviving  and  of 
procreating  their  kind  ?  On  the  other  hand,  we  may  feel  sure  that 
any  variation  in  the  least  degree  injurious  would  be  rigidly  destroyed. 
This  preservation  of  favorable  individual  differences  and  variations, 
and  the  destruction  of  those  which  are  injurious,  I  have  called 
Natural  Selection,  or  the  Survival  of  the  Fittest.  Variations  neither 
useful  nor  injurious  would  not  be  affected  by  natural  selection,  and 
would  be  left  either  a  fluctuating  element,  as  perhaps  we  see  in  certain 
polymorphic  species,  or  would  ultimately  become  fixed,  owing  to  the 
nature  of  the  organism  and  the  nature  of  the  conditions. 

Several  writers  have  misapprehended  or  objected  to  the  term 
Natural  Selection.  Some  have  even  imagined  that  natural  selection 
induces  variability,  whereas  it  implies  only  the  preservation  of  such 
variations  as  arise  and  are  beneficial  to  the  being  under  its  conditions 
of  life.  No  one  objects  to  agriculturists  speaking  of  the  potent  effects 
of  man's  selection;  and  in  this  case  the  individual  differences  given  by 
nature,  which  man  for  some  object  selects,  must  of  necessity  first 
occur.  Others  have  objected  that  the  term  selection  implies  conscious 
choice  in  the  animals  which  become  modified ;  and  it  has  even  been 
urged  that,  as  plants  have  no  voUtion,  natural  selection  is  not  applic- 
able to  them!  In  the  literal  sense  of  the  word,  no  doubt,  natural 
selection  is  a  false  term;  but  who  ever  objected  to  chemists  speaking 
of  the  elective  affinities  of  the  various  elements? — and  yet  an  acid 
cannot  strictly  be  said  to  elect  the  base  with  which  it  in  preference 
combines.  It  has  been  said  that  I  speak  of  natural  selection  as  an 
active  power  or  Deity;  but  who  objects  to  an  author  speaking  of  the 
attraction  of  gravity  as  ruling  the  movements  of  the  planets  ?  Every- 
one knows  what  is  meant  and  is  implied  by  such  metaphorical  expres- 


NATURAL  SELECTION 


225 


sions;  and  they  are  almost  necessary  for  brevity.  So  again  it  is 
difficult  to  avoid  personifying  the  word  Nature;  but  I  mean  by  Nature 
only  the  aggregate  action  and  product  of  many  natural  laws,  and  by 
laws  the  sequence  of  events  as  ascertained  by  us.  With  a  little  famili- 
arity such  superficial  objections  will  be  forgotten. 

We  shall  best  understand  the  probable  course  of  natural  selection 
by  taking  the  case  of  a  country  undergoing  some  slight  physical  change, 
for  instance,  of  climate.  The  proportional  numbers  of  its  inhabitants 
will  almost  immediately  undergo  a  change,  and  some  species  will  prob- 
ably become  extinct.  We  may  conclude,  from  what  we  have  seen  of 
the  intimate  and  complex  manner  in  which  the  inhabitants  of  each 
country  are  bound  together,  that  any  change  in  the  numerical  pro- 
portions of  the  inhabitants,  independently  of  the  change  of  climate 
itself,  would  seriously  affect  the  others.  If  the  country  were  open 
on  its  borders,  new  forms  would  certainly  immigrate,  and  this  would 
likewise  seriously  disturb  the  relations  of  some  of  the  former  inhabi- 
tants. Let  it  be  remembered  how  powerful  the  influence  of  a  single 
introduced  tree  or  mammal  has  been  shown  to  be.  But  in  the  case  of 
an  island,  or  of  a  country  partly  surrounded  by  barriers,  into  which 
new  and  better  adapted  forms  could  not  freely  enter,  we  should  then 
have  places  in  the  economy  of  nature  which  would  assuredly  be 
better  filled  up,  if  some  of  the  original  inhabitants  were  in  some 
manner  modified;  for,  had  the  area  been  open  to  immigration,  these 
same  places  would  have  been  seized  on  by  intruders.  In  such 
cases,  slight  modifications,  which  in  any  way  favored  the  individuals 
of  any  species  by  better  adapting  them  to  their  altered  conditions, 
would  tend  to  be  preserved;  and  natural  selection  would  have  free 
scope  for  the  work  of  improvement. 

We  have  good  reason  to  believe,  as  shown  in  the  first  chapter,  that 
changes  in  the  conditions  of  life  give  a  tendency  to  increased  variability 
and  in  the  foregoing  cases  the  conditions  have  changed,  and  this  would 
manifestly  be  favorable  to  natural  selection,  by  affording  a  better 
chance  of  the  occurrence  of  profitable  variations.  Unless  such  occur, 
natural  selection  can  do  nothing.  Under  the  term  of  "variations,"  it 
must  never  be  forgotten  that  mere  individual  differences  are  included. 
As  man  can  produce  a  great  result  with  his  domestic  animals  and  plants 
by  adding  up  in  any  given  direction  individual  differences,  so  could 
natural  selection,  but  far  more  easily  from  having  incomparably  longer 
time  for  action.  Nor  do  I  believe  that  any  great  physical  change,  as 
of  climate,  or  any  unusual  degree  of  isolation  to  check  immigration. 


2  26      READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

is  necessary  in  order  that  new  and  unoccupied  places  should  be  left, 
for  natural  selection  to  fill  up  by  improving  some  of  the  varying 
inhabitants.  For  as  all  the  inhabitants  of  each  country  are  struggling 
together  with  nicely  balanced  forces,  extremely  slight  modifications  in 
the  structure  or  habits  of  one  species  would  often  give  it  an  advantage 
over  others;  and  still  further  modifications  of  the  same  kind  would 
often  still  further  increase  the  advantage,  as  long  as  the  species  con- 
tinued under  the  same  conditions  of  life  and  profited  by  similar  means 
of  subsistence  and  defense.  No  country  can  be  named  in  which  all  the 
native  inhabitants  are  now  so  perfectly  adapted  to  each  other  and  to 
the  physical  conditions  under  which  they  live,  that  none  of  them  could 
be  still  better  adapted  or  improved;  for  in  all  countries,  the  natives 
have  been  so  far  conquered  by  naturalized  productions,  that  they  have 
allowed  some  foreigners  to  take  firm  possession  of  the  land.  And  as 
foreigners  have  thus  in  every  country  beaten  some  of  the  natives,  we 
may  safely  conclude  that  the  natives  might  have  been  modified  with 
advantage,  so  as  to  have  better  resisted  the  intruders. 

As  man  can  produce,  and  certainly  has  produced,  a  great  result  by 
his  methodical  and  unconscious  means  of  selection,  what  may  not 
natural  selection  effect?  Man  can  act  only  on  external  and  visible 
characters:  Nature,  if  I  may  be  allowed  to  personify  the  natural  pres- 
ervation or  survival  of  the  fittest,  cares  nothing  for  appearances, 
except  in  so  far  as  they  are  useful  to  any  being.  She  can  act  on  every 
internal  organ,  on  every  shade  of  constitutional  difference,  on  the 
whole  machinery  of  life.  Man  selects  only  for  his  own  good :  Nature 
only  for  that  of  the  being  which  she  tends.  Every  selected  character 
is  fully  exercised  by  her,  as  is  implied  by  the  fact  of  their  selection. 
Man  keeps  the  natives  of  many  climates  in  the  same  country;  he 
seldom  exercises  each  selected  character  in  some  peculiar  and  fitting 
manner;  he  feeds  a  long-  and  a  short-beaked  pigeon  on  the  same  food; 
he  does  not  exercise  a  long-backed  or  long-legged  quadruped  in  any 
peculiar  manner;  he  exposes  sheep  with  long  and  short  wool  to  the 
same  climate.  He  does  not  allow  the  most  vigorous  males  to  struggle 
for  the  females.  He  does  not  rigidly  destroy  all  inferior  animals,  but 
protects  during  each  varying  season,  as  far  as  lies  in  his  power,  all 
his  productions.  He  often  begins  his  selection  by  some  half-monstrous 
form;  or  at  least  by  some  modification  prominent  enough  to  catch  the 
eye  or  to  be  plainly  useful  to  him.  Under  nature,  the  slightest  differ- 
ences of  structure  or  constitution  may  well  turn  the  nicely  balanced 
scale  in  the  struggle  for  life,  and  so  be  preserved.    How  fleeting  are  the 


NATURAL  SELF.CTION  227 

wishes  and  efforts  of  man!  how  short  his  time!  and  consequently  how 
poor  will  be  his  results,  compared  with  those  accumulated  by  Nature 
during  whole  geological  periods!  Can  we  wonder,  then,  that  Nature's 
productions  should  be  far"  truer  "in  character  than  man's  productions; 
that  they  should  be  infinitely  better  adapted  to  the  most  complex 
conditions  of  life,  and  should  plainly  bear  the  stamp  of  far  higher 
workmanship  ? 

It  may  metaphorically  be  said  that  natural  selection  is  daily  and 
hourly  scrutinizing,  throughout  the  world,  the  slightest  variations; 
rejecting  those  that  are  bad,  preserving  and  adding  up  all  that  are 
good;  silently  and  insensibly  working  whenever  and  wherever  oppor- 
tunity offers,  at  the  improvement  of  each  organic  being  in  relation  to 
its  organic  and  inorganic  conditions  of  life.  We  see  nothing  of  these 
slow  changes  in  progress,  until  the  hand  of  time  has  marked  the  lapse 
of  ages,  and  then  so  imperfect  is  our  view  into  long-past  geological 
ages,  that  we  see  only  that  the  forms  of  life  are  now  different  from  what 
they  formerly  were. 

In  order  that  any  great  amount  of  modification  should  be  effected 
in  a  species,  a  variety  when  once  formed  must  again,  perhaps  after  a 
long  interval  of  time,  vary  or  present  individual  differences  of  the  same 
favorable  nature  as  before;  and  these  must  be  again  preserved,  and 
so  onwards  step  by  step.  Seeing  that  individual  differences  of  the 
same  kind  perpetually  recur,  this  can  hardly  be  considered  as  an 
unwarrantable  assumption.  But  whether  it  is  true,  we  can  judge  only 
by  seeing  how  far  the  hypothesis  accords  with  and  explains  the  general 
phenomena  of  nature.  On  the  other  hand,  the  ordinary  belief  that 
the  amount  of  possible  variation  is  a  strictly  limited  quantity  is  like- 
wise a  simple  assumption. 

Although  natural  selection  can  act  only  through  and  for  the  good 
of  each  being,  yet  characters  and  structures,  which  we  are  apt  to  con- 
sider as  of  very  trifling  importance,  may  thus  be  acted  on.  When  we 
see  leaf-eating  insects  green,  and  bark-feeders  mottled-gray;  the 
alpine  ptarmigan  white  in  winter,  the  red-grouse  the  color  of  heather, 
we  must  believe  that  these  tints  are  of  service  to  these  birds  and 
insects  in  preserving  them  from  danger.  Grouse,  if  not  destroyed  at 
some  period  of  their  lives,  would  increase  in  countless  numbers;  they 
are  known  to  suffer  largely  from  birds  of  prey;  and  hawks  are  guided 
by  eyesight  to  their  prey — so  much  so,  that  on  parts  of  the  Continent 
persons  are  warned  not  to  keep  white  pigeons,  as  being  the  most  liable 
to  destruction.     Hence  natural  selection  might  be  effective  in  giving 


22S     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

the  proper  color  to  each  kind  of  grouse,  and  in  keeping  that  color, 
when  once  acquired,  true  and  constant.  Nor  ought  we  to  think  that 
the  occasional  destruction  of  an  animal  of  any  particular  color  would 
produce  little  effect:  we  should  remember  how  essential  it  is  in  a  flock 
of  white  sheep  to  destroy  a  lamb  with  the  faintest  trace  of  black.  We 
have  seen  how  the  color  of  the  hogs,  which  feed  on  the  '^paint-root'* 
in  Virginia,  determines  whether  they  shall  live  or  die.  In  plants,  the 
down  on  the  fruit  and  the  color  of  the  flesh  are  considered  by  botanists 
as  characters  of  the  most  trifling  importance:  yet  we  hear  from  an 
excellent  horticulturist.  Downing,  that  in  the  United  States  smooth- 
skinned  fruits  suffer  far  more  from  a  beetle,  a  Curculio,  than  those  with 
down;  that  purple  plums  suffer  far  more  from  a  certain  disease  than 
yellow  plums;  whereas  another  disease  attacks  yellow-fleshed  peaches 
far  more  than  those  with  other  colored  flesh.  If,  with  all  the  aids  of 
art,  these  slight  differences  make  a  great  difference  in  cultivating  the 
several  varieties,  assuredly,  in  a  state  of  nature,  where  the  trees  would 
have  to  struggle  with  other  trees  and  with  a  host  of  enemies,  such  dif- 
ferences would  effectually  settle  which  variety,  whether  a  smooth  or 
downy,  a  yellow-  or  purple-fleshed  fruit,  should  succeed. 

In  looking  at  many  small  points  of  difference  between  species, 
which,  as  far  as  our  ignorance  permits  us  to  judge,  seem  quite  unim- 
portant, we  must  not  forget  that  climate,  food,  etc.,  have  no  doubt 
produced  some  direct  effect.  It  is  also  necessary  to  bear  in  mind  that, 
owing  to  the  law  of  correlation,  when  one  part  varies,  and  the  varia- 
tions are  accumulated  through  natural  selection,  other  modifications, 
often  of  the  most  unexpected  nature,  will  ensue. 

As  we  see  that  those  variations  which,  under  domestication,  appear 
at  any  particular  period  of  life,  tend  to  reappear  in  the  offspring  at  the 
same  period;  for  instance,  in  the  shape,  size,  and  flavor  of  the  seeds 
of  the  many  varieties  of  our  culinary  and  agricultural  plants;  in  the 
caterpillar  and  cocoon  stages  of  the  varieties  of  the  silk-worm ;  in 
the  eggs  of  poultry,  and  in  the  color  of  the  down  of  their  chickens;  in 
the  horns  of  our  sheep  and  cattle  when  nearly  adult;  so  in  a  state  of 
nature  natural  selection  will  be  enabled  to  act  on  and  modify  organic 
beings  at  any  age,  by  the  accumulation  of  variations  profitable  at  that 
age,  and  by  their  inheritance  at  a  corresponding  age.  If  it  profit  a 
plant  to  have  its  seeds  more  and  more  widely  disseminated  by  the 
wind,  I  can  see  no  greater  difficulty  in  this  being  effected  through 
natural  selection,  than  in  the  cotton-planter  increasing  and  improving 
by  selection  the  down  in  the  pods  on  his   cotton-trees.     Natural 


NATURAL  SELECTION  229 

selection  may  modify  and  adapt  the  larva  of  an  insect  to  a  score  of 
contingencies,  wholly  different  from  those  which  concern  the  mature 
insect;  and  these  modifications  may  affect,  through  correlation,  the 
structure  of  the  adult.  So,  conversely,  modifications  in  the  adult  may 
affect  the  structure  of  the  larva;  but  in  all  cases  natural  selection  will 
ensure  that  they  shall  not  be  injurious:  for  if  they  were  so,  the  species 
would  become  extinct. 

Natural  selection  will  modify  the  structure  of  the  young  in  relation 
to  the  parent,  and  of  the  parent  in  relation  to  the  young.  In  social 
animals  it  will  adapt  the  structure  of  each  individual  for  the  benefit  of 
the  whole  community,  if  the  community  profits  by  the  selected 
change.  What  natural  selection  cannot  do,  is  to  modify  the  structure 
of  one  species,  without  giving  it  any  advantage,  for  the  good  of  another 
species;  and  though  statements  to  this  effect  may  be  found  in  works 
of  natural  history,  I  cannot  find  one  case  which  will  bear  investigation. 
A  structure  used  only  once  in  an  animal's  life,  if  of  high  importance 
to  it,  might  be  modified  to  any  extent  by  natural  selection ;  for  instance 
the  great  jaws  possessed  by  certain  insects,  used  exclusively  for  open- 
ing the  cocoon — or  the  hard  tip  to  the  beak  of  unhatched  birds,  used 
for  breaking  the  egg.  It  has  been  asserted,  that  of  the  best  short- 
beaked  tumbler-pigeons  a  greater  number  perish  in  the  egg  than  are 
able  to  get  out  of  it;  so  that  fanciers  assist  in  the  act  of  hatching. 
Now  if  nature  had  to  make  the  beak  of  a  full-grown  pigeon  very 
short  for  the  bird's  own  advantage,  the  process  of  modification  would 
be  very  slow,  and  there  would  be  simultaneously  the  most  rigorous 
selection  of  all  the  young  birds  within  the  egg,  which  had  the  most 
powerful  and  hardest  beaks,  for  all  with  weak  beaks  would  inevitably 
perish;  or,  more  delicate  and  more  easily  broken  shells  might  be 
selected,  the  thickness  of  the  shell  being  known  to  vary  like  every 
other  structure. 

It  may  be  well  here  to  remark  that  with  all  beings  there  must  be 
much  fortuitous  destruction,  which  can  have  little  or  no  influence  on 
the  course  of  natural  selection.  For  instance  a  vast  number  of  eggs 
or  seeds  are  annually  devoured,  and  these  could  be  modified  through 
natural  selection  only  if  they  varied  in  some  manner  which  protected 
them  from  their  enemies.  Yet  many  of  these  eggs  or  seeds  would 
perhaps,  if  not  destroyed,  have  yielded  individuals  better  adapted  to 
their  conditions  of  life  than  any  of  those  which  happened  to  survive. 
So  again  a  vast  number  of  mature  animals  and  plants,  whether  or 
not  they  be  the  best  adapted  to  their  conditions,  must  be  annually 


230     READINGS  IX  EVOLUTION,  GENETICS,  AND  EUGENICS 

destroyed  by  accidental  causes,  which  would  not  be  in  the  least  degree 
mitigated  by  certain  changes  of  structure  or  constitution  which  w^ould 
in  other  ways  be  beneficial  to  the  species.  But  let  the  destruction  of 
the  adults  be  ever  so  heavy,  if  the  number  which  can  exist  in  any 
district  be  not  wholly  kept  down  by  such  causes,  or  again  let  the 
destruction  of  eggs  or  seeds  be  so  great  that  only  a  hundredth  or  a 
thousandth  part  are  developed,  yet  of  those  which  do  survive,  the 
best  adapted  individuals,  supposing  that  there  is  any  variability  in  a 
favorable  direction,  will  tend  to  propagate  their  kind  in  larger  numbers 
than  the  less  well  adapted.  If  the  numbers  be  wholly  kept  down  by 
the  causes  just  indicated,  as  will  often  have  been  the  case,  natural 
selection  will  be  powerless  in  certain  beneficial  directions;  but  this  is 
no  valid  objection  to  its  efficiency  at  other  times  and  in  other  ways; 
for  we  are  far  from  having  any  reason  to  suppose  that  many  species 
ever  undergo  modification  and  improvement  at  the  same  time  in  the 
same  area. 

SEXUAL    SELECTION 

Inasmuch  as  peculiarities  often  appear  under  domestication  in  one 
sex  and  become  hereditarily  attached  to  that  sex,  so  no  doubt  it  will 
be  under  nature.  Thus  it  is  rendered  possible  for  the  two  sexes  to  be 
modified  through  natural  selection  in  relation  to  different  habits  of 
life,  as  is  sometimes  the  case;  or  for  one  sex  to  be  modified  in  relation 
to  the  other  sex,  as  commonly  occurs.  This  leads  me  to  say  a  few 
words  on  what  I  have  called  Sexual  Selection.  This  form  of  selection 
depends,  not  on  a  struggle  for  existence  in  relation  to  other  organic 
beings  or  to  external  conditions,  but  on  a  struggle  between  the  indi- 
viduals of  one  sex,  generally  the  males,  for  the  possession  of  the  other 
sex.  The  result  is  not  death  to  the  unsuccessful  competitor,  but  few 
or  no  offspring.  Sexual  selection  is,  therefore,  less  rigorous  than 
natural  selection.  Generally,  the  most  vigorous  males,  those  which 
are  best  fitted  for  their  places  in  nature,  will  leave  most  progeny. 
But  in  many  cases,  victory  depends  not  so  much  on  general  vigor,  as 
on  having  special  weapons,  confined  to  the  male  sex.  A  hornless 
stag  or  spurless  cock  would  have  a  poor  chance  of  leaving  numerous 
offspring.  Sexual  selection,  by  always  allowing  the  victor  to  breed, 
might  surely  give  indomitable  courage,  length  to  the  spur,  and  strength 
to  the  wing  to  strike  in  the  spurred  leg,  in  nearly  the  same  manner  as 
does  the  brutal  cock-fighter  by  the  careful  selection  of  his  best  cocks. 
How  low  in  the  scale  of  nature  the  law  of  battle  descends,  I  know  not; 
male  alligators  have  been  described  as  fighting,  bellowing,  and  whirl- 


NATURAL  SELECTION 


231 


ing  around,  like  Indians  in  a  war-dance,  for  the  possession  of  the 
females;  male  salmons  have  been  observed  fighting  all  day  long;  male 
stag-beetles  sometimes  bear  wounds  from  the  huge  mandibles  of  other 
males;  the  males  of  certain  hymenopterous  insects  have  been  fre- 
quently seen  by  that  inimitable  observer  M.  Fabre,  fighting  for  a 
particular  female  who  sits  by,  an  apparently  unconcerned  beholder 
of  the  struggle,  and  then  retires  with  the  conqueror.  The  war  is, 
perhaps,  severest  between  the  males  of  polygamous  animals,  and 
these  seem  oftenest  provided  with  special  weapons.  The  males  of 
carnivorous  animals  are  already  well  armed;  though  to  them  and  to 
others,  special  means  of  defense  may  be  given  through  means  of 
sexual  selection,  as  the  mane  of  the  lion,  and  the  hooked  jaw  to  the 
male  salmon;  for  the  shield  may  be  as  important  for  victory  as  the 
sword  or  spear. 

Amongst  birds,  the  contest  is  often  of  a  more  peaceful  character. 
All  those  who  have  attended  to  the  subject  believe  that  there  is  the 
severest  rivalry  between  the  males  of  many  species  to  attract,  by 
singing,  the  females.  The  rock-thrush  of  Guiana,  birds  of  paradise, 
and  some  others,  congregate;  and  successive  males  display  with  the 
most  elaborate  care,  and  show  off  in  the  best  manner,  their  gorgeous 
plumage;  they  likewise  perform  strange  antics  before  the  females, 
which,  standing  by  as  spectators,  at  last  choose  the  most  attractive 
partner.  Those  who  have  closely  attended  to  birds  in  confinement 
well  know  that  they  often  take  individual  preferences  and  dislikes: 
thus  Sir  R.  Heron  has  described  how  a  pied  peacock  was  eminently 
attractive  to  all  his  hen  birds.  I  cannot  here  enter  on  the  necessary 
details;  but  if  man  can  in  a  short  time  give  beauty  and  an  elegant 
carriage  to  his  bantams,  according  to  his  standard  of  beauty,  I  can 
see  no  good  reason  to  doubt  that  female  birds,  by  selecting,  during 
thousands  of  generations,  the  most  melodious  or  beautiful  males, 
according  to  their  standard  of  beauty,  might  produce  a  marked  etTect. 
Some  well-known  laws,  with  respect  to  the  plumage  of  male  and 
female  birds,  in  comparison  with  the  plumage  of  the  young,  can  paflly 
be  explained  through  the  action  of  sexual  selection  on  variations 
occurring  at  different  ages,  and  transmitted  to  the  males  alone  or  to 
both  sexes  at  corresponding  ages;  but  I  have  not  space  here  to  enti?r 
on  this  subject. 

Thus  it  is,  as  I  believe,  that  when  the  males  and  females  of  any 
animal  have  the  same  general  habits  of  life,  but  ditler  in  structure, 
color,  or  ornament,  such  dift'erences  have  been  mainly  caused  by  sexual 


232     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

selection:  that  is,  by  individual  males  having  had,  in  successive  gen- 
erations, some  slight  advantage  over  other  males,  in  their  weapons, 
means  of  defence,  or  charms,  which  they  have  transmitted  to  their 
male  offspring  alone.  Yet,  I  would  not  wish  to  attribute  all  sexual 
differences  to  this  agency:  for  we  see  in  our  domestic  animals  peculi- 
arities arising  and  becoming  attached  to  the  male  sex,  which  appar- 
ently have  not  been  augmented  through  selection  by  man.  The  tuft 
of  hair  on  the  breast  of  the  wild  turkey-cock  cannot  be  of  any  use,  and 
it  is  doubtful  whether  it  can  be  ornamental  in  the  eyes  of  the  female 
bird;  indeed,  had  the  tuft  appeared  under  domestication,  it  would 
have  been  called  a  monstrosity. 

ILLUSTRATIONS  OF   THE  ACTION  OF  NATURAL  SELECTION,    OR  THE 

SURVIVAL  OF  THE  FITTEST 

In  order  to  make  it  clear  how,  as  I  believe,  natural  selection  acts, 
I  must  beg  permission  to  give  one  or  two  imaginary  illustrations.  Let 
us  take  the  case  of  a  wolf,  which  preys  on  various  animals,  securing 
some  by  craft,  some  by  strength,  and  some  by  fleetness;  and  let  us 
suppose  that  the  fleetest  prey,  a  deer  for  instance,  had  from  any  change 
in  the  country  increased  in  numbers,  or  that  other  prey  had  decreased 
in  numbers,  during  that  season  of  the  year  when  the  wolf  was  hardest 
pressed  for  food.  Under  such  circumstances  the  swiftest  and  slimmest 
wolves  would  have  the  best  chance  of  surviving  and  so  be  preserved  or 
selected,  provided  always  that  they  retained  strength  to  master  their 
prey  at  this  or  some  other  period  of  the  year,  when  they  were  compelled 
to  prey  on  other  animals.  I  can  see  no  more  reason  to  doubt  that  this 
would  be  the  result,  than  that  man  should  be  able  to  improve  the 
fleetness  of  his  greyhounds  by  careful  and  methodical  selection,  or 
by  that  kind  of  unconscious  selection  which  follows  from  each  man 
trying  to  keep  the  best  dogs  without  any  thought  of  modifying  the 
breed.  I  may  add,  that,  according  to  Mr.  Pierce,  there  are  two 
varieties  of  the  wolf  inhabiting  the  Catskill  Mountains,  in  the  United 
States,  one  with  a  light  greyhound-like  form,  which  pursues  deer,  and 
the  other  more  bulky,  with  shorter  legs,  which  more  frequently  attacks 
the  shepherd's  flocks. 

It  should  be  observed  that,  in  the  above  illustration,  I  speak  of  the 
slimmest  individual  wolves,  and  not  of  any  single  strongly  marked 
variation  having  been  preserved.  In  former  editions  of  this  work  I 
sometimes  spoke  as  if  this  latter  alternative  had  frequently  occurred. 
I  saw  the  great  importance  of  individual  differences,  and  this  led  me 
fully  to  discuss  the  results  of  unconscious  selection  by  man,  which 


NATURAL  SELECTION 


233 


depends  on  the  preservation  of  all  the  more  or  less  valuable  individuals, 
and  on  the  destruction  of  the  worst.  I  saw,  also,  that  the  preservation 
in  a  state  of  nature  of  any  occasional  deviation  of  structure,  such  as  a 
monstrosity,  would  be  a  rare  event;  and  that,  if  at  first  preserved,  it 
would  generally  be  lost  by  subsequent  intercrossing  with  ordinary 
individuals.  Nevertheless,  until  reading  an  able  and  valuable  article 
in  the  North  British  Review  (1867),  I  did  not  appreciate  how  rarely 
single  variations,  whether  slight  or  strongly  marked,  could  be  per- 
petuated. The  author  takes  the  case  of  a  pair  of  animals,  producing 
during  their  lifetime  two  hundred  offspring,  of  which,  from  various 
causes  of  destruction,  only  two  on  an  average  survive  to  pro-create 
their  kind.  This  is  rather  an  extreme  estimate  for  most  of  the  higher 
animals,  but  by  no  means  so  for  many  of  the  lower  organisms.  He 
then  shows  that  if  a  single  individual  were  born,  which  varied  in  some 
manner,  giving  it  twice  as  good  a  chance  of  life  as  that  of  the  other 
individuals,  yet  the  chances  would  be  strongly  against  its  survival. 
Supposing  it  to  survive  and  to  breed,  and  that  half  its  young  inherited 
the  favorable  variation;  still,  as  the  Reviewer  goes  on  to  show,  the 
young  would  have  only  a  slightly  better  chance  of  surviving  and  breed- 
ing; and  this  chance  would  go  on  decreasing  in  the  succeeding  genera- 
tions. The  justice  of  these  remarks  cannot,  I  think,  be  disputed. 
If,  for  instance,  a  bird  of  some  kind  could  procure  its  food  more  easily 
by  having  its  beak  curved,  and  if  one  were  born  with  its  beak  strongly 
curved,  and  which  consequently  flourished,  nevertheless  there  would 
be  a  very  poor  chance  of  this  one  individual  perpetuating  its  kind  to 
the  exclusion  of  the  common  form;  but  there  can  hardly  be  a  doubt, 
judging  by  what  we  see  taking  place  under  domestication,  that  this 
result  would  follow  from  the  preservation  during  many  generations  of 
a  large  number  of  individuals  with  more  or  less  strongly  curved  beaks, 
and  from  the  destruction  of  a  still  larger  number  with  the  straightest 
beaks. 

SUMMARY   OF    CHAPTER    ON    NATURAL   SELECTION 

If  under  changing  conditions  of  life  organic  beings  present  indi- 
vidual differences  in  almost  every  part  of  their  structure,  and  this 
cannot  be  disputed;  if  there  be,  owing  to  their  geometrical  rale  of 
increase,  a  severe  struggle  for  life  at  some  age,  season,  or  year,  and 
this  certainly  cannot  be  disputed;  then,  considering  the  infinite  com- 
plexity of  the  relations  of  all  organic  beings  to  each  other  and  to  their 
conditions  of  life,  causing  an  infinite  diversity  in  structure,  constitu- 
tion, and  habits,  to  be  advantageous  to  them,  it  would  be  a  most 


234     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

extraordinary  fact  if  no  variations  had  ever  occurred  useful  to  each 
being's  own  welfare,  in  the  same  manner  as  so  many  variations  have 
occurred  useful  to  man.  But  if  variations  useful  to  any  organic  being 
ever  do  occur,  assuredly  individuals  thus  characterized  will  have  the 
best  chance  of  being  preserved  in  the  struggle  for  life;  and  from  the 
strong  principle  of  inheritance,  these  will  tend  to  produce  offspring 
similarly  characterized.  This  principle  of  preservation,  or  the  survival 
of  the  fittest,  I  have  called  Natural  Selection.  It  leads  to  the  im- 
provement of  each  creature  in  relation  to  its  organic  and  inorganic 
conditions  of  life;  and  consequently,  in  most  cases,  to  what  must  be 
regarded  as  an  advance  in  organization.  Nevertheless,  low  and  simple 
forms  will  long  endure  if  well  fitted  for  their  simple  conditions  of  life. 

Natural  selection,  on  the  principle  of  qualities  being  inherited  at 
corresponding  ages,  can  modify  the  egg,  seed,  or  young,  as  easily  as 
the  adult.  Amongst  many  animals,  sexual  selection  will  have  given 
its  aid  to  ordinary  selection,  by  assuring  to  the  most  vigorous  and  best 
adapted  males  the  greatest  number  of  offspring.  Sexual  selection  will 
also  give  characters  useful  to  the  males  alone,  in  their  struggles  or 
rivalry  with  other  males;  and  these  characters  will  be  transmitted  to 
one  sex  or  to  both  sexes,  according  to  the  form  of  inheritance  which 
prevails. 

Whether  natural  selection  has  really  thus  acted  in  adapting  the 
various  forms  of  life  to  their  several  conditions  and  stations,  must  be 
judged  by  the  general  tenor  and  balance  of  evidence  given  in  the  follow- 
ing chapters.  But  we  have  already  seen  how  it  entails  extinction;  and 
how  largely  extinction  has  acted  in  the  world's  history,  geology  plainly 
declares.  Natural  selection,  also,  leads  to  divergence  of  character; 
for  the  more  organic  beings  diverge  in  structure,  habits,  and  constitu- 
tion, by  so  much  the  more  can  a  large  number  be  supported  on  the 
area,  of  which  we  see  proof  by  looking  to  the  inhabitants  of  any 
small  spot,  and  to  the  productions  naturalized  in  foreign  lands.  There- 
fore, during  the  modification  of  the  descendants  of  any  one  species, 
and  during  the  incessant  struggle  of  all  species  to  increase  in  number, 
the  more  diversified  the  descendants  become,  the  better  will  be  their 
chance  of  success  in  the  battle  for  life.  Thus  the  small  differences  dis- 
tinguishing varieties  of  the  same  species,  steadily  tend  to  increase,  till 
they  equal  the  greater  differences  between  species  of  the  same  genus, 
or  even  of  distinct  genera. 

We  have  seen  that  it  is  the  common,  the  widely-diffused  and 
widely  ranging  species,  belonging  to  the  larger  genera  within  each 


NATURAL  SELECTION  2.^5 

class,  which  vary  most;  and  these  tend  to  transmit  to  their  modified 
offspring  that  superiority  which  now  makes  them  dominant  in  their 
own  countries.  Natural  selection,  as  has  just  been  remarked,  leads 
to  divergence  of  character  and  to  much  extinction  of  the  less  improved 
and  intermediate  forms  of  life.  On  these  principles,  the  nature  of  the 
affinities,  and  the  generally  well-defined  distinctions  between  the 
innumerable  organic  beings  in  each  class  throughout  the  world,  may 
be  explained.  It  is  a  truly  wonderful  fact — the  wonder  of  which  we 
are  apt  to  overlook  from  familiarity — that  all  animals  and  all  plants 
throughout  all  time  and  space  should  be  related  to  each  other  in  groups 
subordinate  to  groups,  in  the  manner  which  we  everywhere  behold — 
namely,  varieties  of  the  same  species  rqost  closely  related,  species  of 
the  same  genus  less  closely  and  unequally  related,  forming  sections 
and  sub-genera,  species  of  distinct  genera  much  less  closely  related, 
and  genera  related  in  different  degrees,  forming  sub-families,  families, 
orders,  sub-classes  and  classes.  The  several  subordinate  groups  in  any 
class  cannot  be  ranked  in  a  single  file,  but  seem  clustered  round  points, 
and  these  round  other  points,  and  so  on  in  almost  endless  cycles.  If 
species  had  been  independently  created,  no  explanation  would  have 
been  possible  of  this  kind  of  classification;  but  it  is  explained  through 
inheritance  and  the  complex  action  of  natural  selection,  entailing 
extinction  and  divergence  of  character,  as  we  have  seen  illustrated  in 
the  diagram. 

The  affinities  of  all  the  beings  of  the  same  class  have  sometimes 
been  represented  by  a  great  tree.  I  believe  this  simile  largely  speaks 
the  truth.  The  green  and  budding  twigs  may  represent  existing 
species;  and  those  produced  during  former  years  may  represent  the 
long  succession  of  extinct  species.  At  each  period  of  growth  all  the 
growing  twigs  have  tried  to  branch  out  on  all  sides,  and  to  overtop  and 
kill  the  surrounding  twigs  and  branches,  in  the  same  manner  as  species 
and  groups  of  species  have  at  all  times  overmastered  other  species  in 
the  great  battle  for  life.  The  limbs  divided  into  great  branches,  and 
these  into  lesser  and  lesser  branches,  were  themselves  once,  when  the 
tree  was  young,  budding  twigs;  and  this  connection  of  the  former  and 
present  buds  by  ramifying  branches  may  well  represent  the  classifica- 
tion of  all  extinct  and  living  species  in  groups  subordinate  to  groups. 
Of  the  many  twigs  which  flourished  when  the  tree  was  a  mere  bush, 
only  two  or  three,  now  grown  into  great  branches,  yet  survive  and  bear 
the  other  branches;  so  with  the  species  which  lived  during  long-past 
geological  periods,  very  few  have  left  living  and  modified  descendants. 


236     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

From  the  first  growth  of  the  tree,  many  a  Hmb  and  branch  has  decayed 
and  dropped  off;  and  these  fallen  branches  of  various  sizes  may  repre- 
sent those  whole  orders,  families,  and  genera  which  have  now  no  living 
representatives,  and  which  are  known  to  us  only  in  a  fossil  state.  As 
we  here  and  there  see  a  thin  straggling  branch  springing  from  a  fork 
low  down  in  a  tree,  and  which  by  some  chance  has  been  favored  and  is 
still  alive  on  its  summit,  so  we  occasionally  see  an  animal  like  the 
Ornithorh}mchus  or  Lepidosiren,  which  in  some  small  degree  connects 
by  its  affinities  two  large  branches  of  life,  and  which  has  apparently 
been  saved  from  fatal  competition  by  having  inhabited  a  protected 
station.  As  buds  give  rise  by  growth  to  fresh  buds,  and  these,  if 
vigorous,  branch  out  and  overtop  on  all  sides  many  a  feebler  branch, 
so  by  generation  I  believe  it  has  been  with  the  great  Tree  of  Life,  which 
fills  with  its  dead  and  broken  branches  the  crust  of  the  earth,  and 
covers  the  surface  with  its  ever-branching  and  beautiful  ramifications. 

DIFFICULTIES   AND   OBJECTIONS   TO   NATURAL   SELECTION   AS 

SEEN   BY  DARWIN 

Long  before  the  reader  has  arrived  at  this  part  of  my  work,  a  crowd 
of  difficulties  will  have  occurred  to  him.  Some  of  them  are  so  serious 
that  to  this  day  I  can  hardly  reflect  on  them  without  being  in  some 
degree  staggered;  but,  to  the  best  of  my  judgment,  the  greater  number 
are  only  apparent,  and  those  that  are  real  are  not,  I  think,  fatal  to  the 
theory. 

These  difficulties  and  objections  may  be  classed  under  the  follow- 
ing heads:  First,  why,  if  species  have  descended  from  other  species 
by  fine  gradations,  do  we  not  everywhere  see  innumerable,  transitional 
forms?  Why  is  not  all  nature  in  confusion,  instead  of  the  species 
being,  as  we  see  them,  well  defined  ? 

Secondly,  is  it  possible  that  an  animal  having,  for  instance,  the 
structure  and  habits  of  a  bat,  could  have  been  formed  by  the  modifica- 
tion of  some  other  animal  with  widely  different  habits  and  structure  ? 
Can  we  believe  that  natural  selection  could  produce,  on  the  one  hand, 
an  organ  of  trifling  importance,  such  as  the  tail  of  a  giraffe,  which 
serves  as  a  fly-flapper,  and,  on  the  other  hand,  an  organ  so  wonderful 
as  the  eye  ? 

Thirdly,  can  instincts  be  acquired  and  modified  through  natural 
selection  ?  What  shall  we  say  to  the  instinct  which  leads  the  bee  to 
make  cells,  and  which  has  practically  anticipated  the  discoveries  of 
profound  mathematicians  ? 


NATURAL  SELECTION  237 

Fourthly,  how  can  we  account  for  species,  when  crossed,  being 
sterile  and  producing  sterile  offspring,  whereas,  when  varieties  are 
crossed,  their  fertility  is  unimpaired  ? 

ANSWER   TO    THE    FIRST   DIFFICULTY 

On  the  Absence  or  Rarity  of  Transitional  Varieties, — As  natural 
selection  acts  solely  by  the  preservation  of  profitable  modifications, 
each  new  form  will  tend  in  a  fully  stocked  country  to  take  the  place  of, 
and  finally  to  exterminate,  its  own  less  improved  parent-form  and 
other  less-favored  forms  with  which  it  comes  into  competition.  Thus 
extinction  and  natural  selection  go  hand  in  hand.  Hence,  if  we  look 
at  each  species  as  descended  from  some  unknown  form,  both  the  parent 
and  all  the  transitional  varieties  will  generally  have  been  exterminated 
by  the  very  process  of  the  formation  and  perfection  of  the  new 
form. 

But,  as  by  this  theory  innumerable  transitional  forms  must  have 
existed,  why  do  we  not  find  them  embedded  in  countless  numbers  in 
the  crust  of  the  earth?  It  will  be  more  convenient  to  discuss  this 
question  in  the  chapter  on  the  Imperfection  of  the  Geological  Record; 
and  I  will  here  only  state  that  I  beheve  the  answer  mainly  lies  in  the 
record  being  incomparably  less  perfect  than  is  generally  supposed. 
The  crust  of  the  earth  is  a  vast  museum;  but  the  natural  collections 
have  been  imperfectly  made,  and  only  at  long  intervals  of  time. 

ANSWER  TO  THE   SECOND  DIFFICULTY:     ORGANS  OF  EXTREME 
PERFECTION  AND  COMPLICATION 

To  suppose  that  the  eye  with  all  its  inimitable  contrivances  for 
adjusting  the  focus  to  different  distances,  for  admitting  different 
amounts  of  light,  and  for  the  correction  of  spherical  and  chromatic 
aberration,  could  have  been  formed  by  natural  selection,  seems,  I 
freely  confess,  absurd  in  the  highest  degree.  When  it  was  first  said 
that  the  sun  stood  still  and  the  world  turned  round,  the  common  sense 
of  mankind  declared  the  doctrine  false;  but  the  old  saying  of  Vox 
populi,  vox  Dei,  as  every  philosopher  knows,  cannot  be  trusted  in 
science.  Reason  tells  me,  that  if  numerous  gradations  from  a  simple 
and  imperfect  eye  to  one  complex  and  perfect  can  be  shown  to  exist, 
each  grade  being  useful  to  its  possessor,  as  is  certainly  the  case;  if 
further,  the  eye  varies  and  the  variations  be  inherited,  as  is  likewise 
certainly  the  case;  and  if  such  variations  should  be  useful  to  any  ani- 
mal under  changing  conditions  of  life,  then  the  difficulty  of  believing 


238     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

that  a  perfect  and  complex  eye  could  be  formed  by  natural  selection, 
though  insuperable  by  our  imagination,  should  not  be  considered  as 
subversive  of  the  theory.  How  a  nerve  comes  to  be  sensitive  to  light, 
hardly  concerns  us  more  than  how  life  itself  originated;  but  I  may 
remark  that,  as  some  of  the  lowest  organisms,  in  which  nerves  cannot 
be  detected,  are  capable  of  perceiving  light,  it  does  not  seem  impossible 
that  certain  sensitive  elements  in  their  sarcode  should  become  aggre- 
gated and  developed  into  nerves,  endowed  with  this  special  sensi- 
bility. 

In  searching  for  the  gradations  through  which  an  organ  in  any 
species  has  been  perfected,  we  ought  to  look  exclusively  to  its  lineal 
progenitors;  but  this  is  scarcely  ever  possible,  and  we  are  forced  to 
look  to  other  species  and  genera  of  the  same  group,  that  is  to  the 
collateral  descendants  from  the  same  parent-form,  in  order  to  see  what 
gradations  are  possible,  and  for  the  chance  of  some  gradations  hav- 
ing been  transmitted  in  an  unaltered  or  little  altered  condition.  But 
the  state  of  the  same  organ  in  distinct  classes  may  incidentally  throw 
light  on  the  steps  by  which  it  has  been  perfected. 

The  simplest  organ  which  can  be  called  an  eye  consists  of  an  optic 
nerve,  surrounded  by  pigment-Cells  and  covered  by  translucent  skin, 
but  without  any  lens  or  other  refractive  body.  We  may,  however, 
according  to  M.  Jourdain,  descend  even  a  step  lower  and  find  aggre- 
gates, of  pigment-cells,  apparently  serving  as  organs  of  vision,  without 
any  nerves,  and  resting  merely  on  sarcodic  tissue.  Eyes  of  the  above 
simple  nature  are  not  capable  of  distinct  vision,  and  serve  only  to  dis- 
tinguish light  from  darkness.  In  certain  star-fishes,  small  depressions 
in  the  layer  of  pigment  which  surrounds  the  nerve  are  filled,  as  de- 
scribed by  the  author  just  quoted,  with  transparent  gelatinous  matter, 
projecting  with  a  convex  surface,  like  the  cornea  in  the  higher  animals. 
He  suggests  that  this  serves  not  to  form  an  image,  but  only  to  con- 
centrate the  luminous  rays  and  render  their  perception  more  easy. 
In  this  concentration  of  the  rays  we  gain  the  first  and  by  far  the  most 
important  step  towards  the  formation  of  a  true,  picture-forming  eye; 
for  we  have  only  to  place  the  naked  extremity  of  the  optic  nerve, 
which  in  some  of  the  lower  animals  lies  deeply  buried  in  the  body,  and 
in  some  near  the  surface,  at  the  right  distance  from  the  concentrating 
apparatus,  and  an  image  will  be  formed  on  it. 

In  the  great  class  of  the  Articulata,  we  may  start  from  an  optic 
nerve  simply  coated  with  pigment,  the  latter  sometimes  forming  a  sort 


NATURAL  SELECTION  239 

of  pupil,  but  destitute  of  a  lens  or  other  optical  contrivance.  With 
insects  it  is  now  known  that  the  numerous  facets  on  the  cornea  of  their 
great  compound  eyes  form  true  lenses,  and  that  the  cones  include 
curiously  modified  nervous  filaments.  But  these  organs  in  the 
Articulata  are  so  much  diversified  that  Muller  formerly  made  three 
main  classes  with  seven  subdivisions,  besides  a  fourth  main  class  of 
aggregated  simple  eyes. 

When  we  reflect  on  these  facts,  here  given  much  too  briefly,  with 
respect  to  the  wide,  diversified,  and  graduated  range  of  structure  in  the 
eyes  of  the  lower  animals;  and  when  we  bear  in  mind  how  small  the 
number  of  all  living  forms  must  be  in  comparison  with  those  which 
have  become  extinct,  the  difliculty  ceases  to  be  very  great  in  believing 
that  natural  selection  may  have  converted  the  simple  apparatus  of  an 
optic  nerve,  coated  with  pigment  and  invested  by  transparent  mem- 
brane, into  an  optical  instrument  as  perfect  as  is  possessed  by  any 
member  of  the  Articulate  Class. 

He  who  will  go  thus  far,  ought  not  to  hesitate  to  go  one  step  fur- 
ther, if  he  finds  on  finishing  this  volume  that  large  bodies  of  facts, 
otherwise  inexplicable,  can  be  explained  by  the  theory  of  modification 
through  natural  selection;  he  ought  to  admit  that  a  structure  even  as 
perfect  as  an  eagle's  eye  might  thus  be  formed,  although  in  this  case 
he  does  not  know  the  transitional  states.  It  has  been  objected  that 
in  order  to  modify  the  eye  and  still  preserve  it  as  a  perfect  instrument, 
many  changes  would  have  to  be  effected  simultaneously,  which,  it  is 
assumed,  could  not  be  done  through  natural  selection;  but  as  I  have 
attempted  to  show  in  my  work  on  the  variation  of  domestic  animals, 
it  is  not  necessary  to  suppose  that  the  modifications  were  all  simulta- 
neous, if  they  were  extremely  slight  and  gradual.  Different  kinds  of 
modification  would,  also,  serve  for  the  same  general  purpose:  as 
Mr.  Wallace  has  remarked,  "if  a  lens  has  too  short  or  too  long  a 
focus,  it  may  be  amended  either  by  an  alteration  of  curvature,  or  an 
alteration  of  density;  if  the  curvature  be  irregular,  and  the  rays  do  not 
converge  to  a  point,  then  any  increased  regularity  of  curvature  will  be 
an  improvement.  So  the  contraction  of  the  iris  and  the  muscular 
movements  of  the  eye  are  neither  of  them  essential  to  vision,  but 
only  improvements  which  might  have  been  added  and  perfected  at  any 
stage  of  the  construction  of  the  instrument.''  Within  the  highest 
division  of  the  animal  kingdon,  namely,  the  Vertebrata,  we  can  start 
from  an  eye  so  simple,  that  it  consists,  as  in  the  lancelet,  of  a  little 


240     READINGS  IN  EVOLUTION,  GENETICS,  AND   EUGENICS 

ck  of  transparent  skin,  furnished  with  a  nerve  and  Hned  with  pig- 
ment, but  destitute  of  any  other  apparatus.  In  fishes  and  reptiles, 
as  Owen  has  remarked,  "  the  range  of  gradations  of  dioptric  structures 
is  very  great. "  It  is  a  significant  fact  that  even  in  man,  according  to 
the  high  authority  of  Virchow,  the  beautiful  crystalline  lens  is  formed 
in  the  embryo  by  an  accumulation  of  epidermic  cells,  lying  in  a  sack- 
like fold  of  the  skin;  and  the  vitreous  body  is  formed  from  embryonic 
sub-cutaneous  tissue.  To  arrive,  however,  at  a  just  conclusion 
regarding  the  formation  of  the  eye,  with  all  its  marvellous  yet  not 
absolutely  perfect  characters,  it  is  indispensable  that  the  reason  should 
conquer  the  imagination;  but  I  have  felt  the  difficulty  far  too  keen 
to  be  surprised  at  others  hesitating  to  extend  the  principle  of 
natural  selection  to  so  startling  a  length. 

It  is  scarcely  possible  to  avoid  comparing  the  eye  with  a  telescope. 
We  know  that  this  instrument  has  been  perfected  by  the  long- 
continued  efforts  of  the  highest  human  intellects;  and  we  naturally 
infer  that  the  eye  has  been  formed  by  a  somewhat  analogous  process. 
But  may  not  this  inference  be  presumptuous  ?  Have  we  any  right  to 
assume  that  the  Creator  works  by  intellectual  powers  like  those  of 
man  ?  If  we  must  compare  the  eye  to  an  optical  instrument,  we  ought 
in  imagination  to  take  a  thick  layer  of  transparent  tissue,  with  spaces 
filled  with  fluid,  and  with  a  nerve  sensitive  to  light  beneath,  and  then 
suppose  every  part  of  this  layer  to  be  continually  changing  slowly  in 
density,  so  as  to  separate  into  layers  of  different  densities  and  thick- 
nesses, placed  at  different  distances  from  each  other,  and  with  the  sur- 
faces of  each  layer  slowly  changing  in  form.  Further  we  must  suppose 
that  there  is  a  power,  represented  by  natural  selection  or  the  survival 
of  the  fittest,  always  intently  watching  each  slight  alteration  in  the 
transparent  layers;  and  carefully  preserving  each  which,  under  varied 
circumstances,  in  any  way  or  in  any  degree,  tends  to  produce  a  dis- 
tincter  image.  We  must  suppose  each  new  state  of  the  instrument  to 
be  multiplied  by  the  million;  each  to  be  preserved  until  a  better  one 
is  produced,  and  then  the  old  ones  to  be  all  destroyed.  In  living 
bodies,  variation  will  cause  the  slight  alterations,  generation  will 
multiply  them  almost  infinitely,  and  natural  selection  will  pick  out 
with  unerring  skill  each  improvement.  Let  this  process  go  on  for 
millions  of  years;  and  during  each  year  on  millions  of  individuals  of 
many  kinds;  and  may  we  not  believe  that  a  living  optical  instrument 
might  thus  be  formed  as  superior  to  one  of  glass,  as  the  works  of  the 
Creator  are  to  those  of  man  ? 


NATURAL  SELECTION  241 

Darwin's  summary  of  his  answer  to  the  third  difficulty,  that  of  accounting 

FOR  THE  acquisition  AND  MODIFICATION  OF  INSTINCTS 
through  natural  SELECTION 

I  have  endeavored  in  this  chapter  briefly  to  show  that  the  mental 
quahties  of  our  domestic  animals  vary,  and  that  the  variations  are 
inherited.  Still  more  briefly  I  have  attempted  to  show  that  instincts 
vary  slightly  in  a  state  of  nature.  No  one  will  dispute  that  instincts 
are  of  the  highest  importance  to  each  animal.  Therefore  there  is  no 
real  difficulty,  under  changing  conditions  of  life,  in  natural  selection 
accumulating  to  any  extent  slight  modifications  of  instinct  which  are 
in  any  way  useful.  In  many  cases  habit  or  use  and  disuse  have  prob- 
ably come  into  play.  I  do  not  pretend  that  the  facts  given  in  this 
chapter  strengthen  in  any  great  degree  my  theory;  but  none  of  the 
cases  of  difficulty,  to  the  best  of  my  judgment,  annihilate  it.  On  the 
other  hand,  the  fact  that  instincts  are  not  always  absolutely  perfect 
and  are  liable  to  mistakes:  that  no  instinct  can  be  shown  to  have  been 
produced  for  the  good  of  other  animals,  though  animals  take  advantage 
of  the  instincts  of  others;  that  the  canon  in  natural  history,  of 
'^Natura  non  facit  saltum,"  is  applicable  to  instincts  as  well  as  to  cor- 
poreal structure,  and  is  plainly  explicable  on  the  foregoing  views,  but 
is  otherwise  inexplicable,  all  tend  to  corroborate  the  theory  of  natural 
selection. 

This  theory  is  also  strengthened  by  some  few  other  facts  in  regard 
to  instincts;  as  by  that  common  case  of  closely  allied,  but  distinct, 
species,  when  inhabiting  distant  parts  of  the  world  and  living  under 
considerably  different  conditions  of  life,  yet  often  retaining  nearly  the 
same  instincts.  For  instance,  we  can  understand,  on  the  principle  of 
inheritance,  how  it  is  that  the  thrush  of  tropical  South  America  lines 
its  nest  with  mud,  in  the  same  pecuHar  manner  as  does  our  British 
thrush;  how  it  is  that  the  Hornbills  of  Africa  and  India  have  the  same 
extraordinary  instinct  of  plastering  up  and  imprisoning  the  females 
in  a  hole  in  a  tree,  with  only  a  small  hole  left  in  the  plaster  through 
which  the  males  feed  them  and  their  young  when  hatched;  how  it  is 
that  the  male  wrens  (Troglodytes)  of  North  America  build  "cock- 
nests,"  to  roost  in,  like  the  males  of  our  Kitty-wrens,  a  habit  wholly 
unlike  that  of  any  other  known  bird.  Finally,  it  may  not  be  a  logical 
deduction,  but  to  my  imagination  it  is  far  more  satisfactory  to  look 
at  such  instincts  as  the  young  cuckoo  ejecting  its  foster-brothers, 
ants  making  slaves,  the  larvae  of  ichneumonidae  feeding  within  the 
live  bodies   of   caterpillars,   not  as   specially   endowed    or   created 


242      READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

instincts,  but  as  small  consequences  of  one  general  law  leading  to  the 
advancement  of  all  organic  beings,  namely,  multiply,  vary,  let  the 
strongest  live  and  the  weakest  die. 

darwin's  summary  of  his  answer  to  the  difficulty  as  to  the  inability  of 

NATURAL  selection  TO  ACCOUNT  FOR  THE  FACT  THAT  SPECIES  WHEN  CROSSED 
ARE  STERILE  OR  PRODUCE  STERILE  OFFSPRING,  WHEREAS  WHEN  VARIETIES 
ARE  CROSSED  THEIR  FERTILITY  IS  UNIMPAIRED 

First  crosses  between  forms,  sufficiently  distinct  to  be  ranked  as 
species,  and  their  hybrids,  are  very  generally,  but  not  universally 
sterile.  The  sterility  is  of  all  degrees,  and  is  often  so  slight  that  the 
most  careful  experimentalists  have  arrived  at  diametrically  opposite 
conclusions  in  ranking  forms  by  this  test.  The  sterility  is  innately 
variable  in  individuals  of  the  same  species,  and  is  eminently  suscept- 
ible to  the  action  of  favorable  and  unfavorable  conditions.  The  degree 
of  sterility  does  not  strictly  follow  systematic  affinity,  but  is  governed 
by  several  curious  and  complex  laws.  It  is  generally  different,  and 
sometimes  widely  different  in  reciprocal  crosses  between  the  same  two 
species.  It  is  not  always  equal  in  degree  in  a  first  cross  and  in  the 
hybrids  produced  from  this  cross. 

In  the  same  manner  as  in  grafting  trees,  the  capacity  in  one  species 
or  variety  to  take  on  another,  is  incidental  on  differences,  generally 
of  an  unknown  nature,  in  their  vegetative  systems,  so  in  crossing,  the 
greater  or  less  facility  of  one  species  to  unite  with  another  is  incidental 
on  unknown  differences  in  their  reproductive  systems.  There  is  no 
more  reason  to  think  that  species  have  been  specially  endowed  with 
various  degrees  of  sterility  to  prevent  their  crossing  and  blending  in 
nature,  than  to  think  that  trees  have  been  specially  endowed  with 
various  and  somewhat  analogous  degrees  of  difficulty  in  being  grafted 
together  in  order  to  prevent  their  inarching  in  our  forests. 

The  sterility  of  first  crosses  and  of  their  hybrid  progeny  has  not 
been  acquired  through  natural  selection.  In  the  case  of  first  crosses 
it  seems  to  depend  on  several  circumstances;  in  some  instances  in 
chief  part  on  the  early  death  of  the  embryo.  In  the  case  of  hybrids, 
it  apparently  depends  on  their  whole  organization  having  been  dis- 
turbed by  being  compounded  from  two  distinct  forms;  the  sterility 
being  closely  allied  to  that  which  so  frequently  affects  pure  species, 
when  exposed  to  new  and  unnatural  conditions  of  life.  He  who  will 
explain  these  latter  cases  will  be  able  to  explain  the  sterility  of  hybrids. 
This  view  is  strongly  supported  by  a  parallelism  of  another  k,ind: 
namely,  that,  firstly,  slight  changes  in  the  conditions  of  life  add  to  the 


NATUR.\L  SELECTION 


243 


vigor  and  fertility  of  all  organic  beings;  and  secondly,  that  the  cross- 
ing of  forms,  which  have  been  exposed  to  slightly  different  conditions 
of  life  or  which  have  varied,  favors  the  size,  vigor,  and  fertility  of  their 
offspring.  The  facts  given  on  the  sterility  of  the  illegitimate  unions 
of  dimorphic  and  trimorphic  plants  and  of  their  illegitimate  progeny, 
perhaps  render  it  probable  that  some  unknown  bond  in  all  cases  con- 
nects the  degree  of  fertility  of  first  unions  with  that  of  their  offspring. 
The  consideration  of  these  facts  on  dimorphism,  as  well  as  of  the  results 
of  reciprocal  crosses,  clearly  leads  to  the  conclusion  that  the  primary 
cause  of  the  sterility  of  crossed  species  is  confined  to  differences  in  their 
sexual  elements.  But  why,  in  the  case  of  distinct  species,  the  sexual 
elements  should  so  generally  have  become  more  or  less  modified,  lead- 
ing to  their  mutual  infertility,  we  do  not  know;  but  it  seems  to  stand  in 
some  close  relation  to  species  having  been  exposed  for  long  periods  of 
time  to  nearly  uniform  conditions  of  life. 

It  is  not  surprising  that  the  difficulty  in  crossing  any  two  species, 
and  the  sterility  of  their  hybrid  offspring,  should  in  most  cases  corre- 
spond, even  if  due  to  distinct  causes:  for  both  depend  on  the  amount 
of  difference  between  the  species  which  are  crossed.  Nor  is  it  sur- 
prising that  the  facility  of  effecting  a  first  cross,  and  the  fertility  of  the 
hybrids  thus  produced,  and  the  capacity  of  being  grafted  together — 
though  this  latter  capacity  evidently  depends  on  widely  different  cir- 
cumstances— should  all  run,  to  a  certain  extent,  parallel  with  the 
systematic  affinity  of  the  forms  subjected  to  experiment;  for  system- 
atic affinity  includes  resemblances  of  all  kinds. 

First  crosses  between  forms  known  to  be  varieties,  or  sufficiently 
alike  to  be  considered  as  varieties,  and  their  mongrel  offspring,  are 
very  generally,  but  not,  as  is  so  often  stated,  invariably  fertile.  Nor 
is  this  almost  universal  and  perfect  fertiUty  surprising,  when  it  is 
remembered  how  liable  we  are  to  argue  in  a  circle  with  respect  to 
varieties  in  a  state  of  nature;  and  when  we  remember  that  the  greater 
number  of  varieties  have  been  produced  under  domestication  by  the 
selection  of  mere  external  differences,  and  that  they  have  not  been 
long  exposed  to  uniform  conditions  of  life.  It  should  also  be  espe- 
cially kept  in  mind  that  long-continued  domestication  tends  to  elimi- 
nate sterility,  and  is  therefore  little  likely  to  induce  this  same  quality. 
Independently  of  the  question  of  fertility,  in  all  other  respects  there 
is  the  closest  general  resemblance  between  hybrids  and  mongrels, 
in  their  variability,  in  their  power  of  absorbing  each  other  by  repeated 
crosses,  and  in  their  inheritance  of  characters  from  both  parent-forms. 


244     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

Finally,  then,  although  we  are  as  ignorant  of  the  precise  cause  of  the 
sterility  of  first  crosses  and  of  hybrids  as  we  are  why  animals  and 
plants  removed  from  their  natural  conditions  become  sterile,  yet  the 
facts  given  in  this  chapter  do  not  seem  to  me  opposed  to  the  belief  that 
species  aboriginally  existed  as  varieties. 


CHAPTER  XVII 

CRITIQUE  OF  DARWINISM 

[The  last  chapter  dealt  with  the  central  ideas  of  Darwin  as  told  by 
himself.  Some  of  the  chief  objections  to  the  theory  were  also  presented 
as  Darwin  saw  them,  and  his  own  answers  to  these  objections  were 
given.  These  four  objections  are  not  by  any  means  all  that  Darwin 
foresaw,  for  he  presented  in  another  chapter  a  discussion  of  "Miscel- 
laneous Objections  to  the  Theory  of  Natural  Selection."  Before 
entering  upon  a  general  criticism  of  Darwinism,  it  would  be  advanta- 
geous to  have  before  us  a  brief  and  pointed  summary  of  Darwin's 
theory — natural  selection — now  known  technically  as  Darwinism. 
The  writer  knows  of  no  better  short  statement  of  the  true  content  of 
Darwinism  than  the  following  summary  by  Professor  Vernon  L. 
Kellogg. — Ed.] 

SUMMARY   OF   DARWIN'S   NATURAL-SELECTION   THEORY' 

VERNON    L.    KELLOGG 

Darwinism  may  be  defined  as  a  certain  rational,  causo-mechanical 
(hence,  non-teleologic)  explanation  of  the  origin  of  new  species.  The 
Darwinian  explanation  rests  on  certain  observed  facts,  and  certain 
inductions  from  these  facts.  The  observed  facts  are:  (i)  the  increase 
by  multiplication  in  geometrical  ratio  of  the  individuals  in  every 
species,  whatever  the  kind  of  reproduction  which  may  be  peculiar  to 
each  species,  whether  this  be  simple  division,  sporulation,  budding, 
parthenogenesis,  conjugation  and  subsequent  division,  or  amphimixis 
(sexual  reproduction);  (2)  the  always  apparent  slight  (to  greater) 
variation  in  form  and  function  existing  among  all  individuals  even 
though  of  the  same  generation  or  brood;  and  (3)  the  transmission, 
with  these  inevitable  slight  variations,  by  the  parent  to  its  offspring 
of  a  form  and  physiology  essentially  like  the  parental.  The  inferred 
(also  partly  observed)  facts  are:  (i)  a  lack  of  room  and  food  for  all 
these  new  individuals  produced  by  geometrical  multiplication  and 
consequently  a  competition  (active  or  passive)  among  those  individuals 
having  any  ecologic  relations  to  one  another,  as,  for  example,  among 

^  From  V.  L.  Kellogg,  Danvinism  To-Day  (copyright  1907).  Used  by  per- 
roission  of  the  publishers,  Henry  Holt  &  Company. 

245 


246      READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

those  occupying  the  same  locaHty,  or  needmg  the  same  food,  or  needing 
each  other  as  food;  (2)  the  probable  success  in  this  competition  of 
those  individuals  whose  slight  differences  (variations)  are  of  such  a 
nature  as  to  give  them  an  advantage  over  their  confreres,  which 
results  in  saving  their  life,  at  least  until  they  have  produced  offspring; 
and  (3)  the  fact  that  these  "saved"  individuals  will,  by  virtue  of  the 
already  referred  to  action  of  heredity,  hand  down  to  the  offspring 
their  advantageous  condition  of  structure  and  physiology  (at  least,  as 
the  ''mode"  or  most  abundantly  represented  condition,  among  the 
offspring). 

The  competition  among  individuals  and  kinds  (species)  of  organ- 
isms may  fairly  be  called  a  struggle.  This  is  obvious  when  it  is  active, 
as  in  actual  personal  battling  for  a  piece  of  food  or  in  attempts  to 
capture  prey  or  to  escape  capture,  and  less  obvious  when  it  is  passive, 
as  in  the  endurance  of  stress  of  weather,  hunger,  thirst,  and  untoward 
conditions  of  any  kind.  The  struggle  is,  or  may  be,  for  each  individual 
threefold  in  nature:  (i)  an  active  struggle  or  competition  with  other 
individuals  of  its  own  kind  for  space  in  the  habitat,  sufficient  share  of 
the  food,  and  opportunity  to  produce  offspring  in  the  way  peculiar 
and  common  to  its  species;  (2)  an  active  or  passive  struggle  or  compe- 
tition with  the  individuals  of  other  species,  which  may  need  the  same 
space  and  food  as  itself,  or  may  need  it  or  its  eggs  or  young  for  food; 
and  (3)  an  active  (or  more  usually  passive)  struggle  with  the  physico- 
chemical  external  conditions  of  the  world  it  lives  in,  as  varying 
temperature  and  humidity,  storms  and  floods,  and  natural  catas- 
trophes of  all  sorts.  For  any  individual  or  group  of  individuals  any  of 
these  forms  of  struggle  may  be  temporarily  ameliorated,  as  is  (i)  the 
intra-specific  struggle  among  the  thousands  of  honey-bee  individuals 
living  together  altruistically,  in  one  hive,  or  (2)  the  inter-specific 
struggle,  when  two  species  live  together  symbiotically  as  the  hermit 
crab  Eupa gurus  and  the  sea-anemone  Podocoryne,  or  (3)  the  struggle 
against  untoward  natural  conditions  as  in  special  times  or  places 
of  highly  favourable  climate,  etc.  Or  for  any  individual  or  group 
of  individuals  all  forms  of  the  struggle  may  be  coincidently  active 
and  severe.  The  resultant  of  these  existing  conditions  is,  accord- 
ing to  Darwin  and  his  followers,  an  inevitable  natural  selection  of 
individuals  and  of  species.  Thousands  must  die  where  one  or  ten 
may  live  to  maturity  (i.e.,  to  the  time  of  producing  young).  Which 
ten  of  the  thousand  shall  live  depends  on  the  slight  but  sufficient 
advantage  possessed  by  ten  individuals  in  the  complex  struggle  for 


CRITIQUE  OF  DARWINISM  247 

existence  due  to  the  fortuitous  possession  of  fortunate  congenital 
differences  (variations).  The  nine  hundred  and  ninety  with  unfortu- 
nate congenital  variations  are  extinguished  in  the  struggle  and  with 
them  the  opportunity  for  the  perpetuation  (by  transmission  to  the 
offspring)  of  their  particular  variations.  There  are  thus  left  ten  to 
reproduce  their  advantageous  variations.  The  offspring  of  the  ten  of 
course  will  vary  in  their  turn,  but  will  vary  around  the  new  and 
already  proved  advantageous  parental  condition:  among  the  thou- 
sand, say,  offspring  of  the  original  saved  ten  the  same  limitations  of 
space  and  food  will  again  work  to  the  killing  off  before  maturity  of 
nine  hundred  and  ninety,  leaving  the  ten  best  equipped  to  reproduce. 
This  repeated  and  intensive  selection  leads  to  a  slow  but  steady  and 
certain  modification  through  the  successive  generations  of  the  form 
and  functions  of  the  species;  a  modification  always  toward  adapta- 
tion, toward  fitness,  toward  a  moulding  of  the  body  and  its  behaviour 
to  safe  conformity  with  external  conditions.  The  exquisite  adapta- 
tion of  the  parts  and  functions  of  the  animal  and  plant  as  we  see  it 
every  day  to  our  infinite  admiration  and  wonder  has  all  come  to  exist 
through  the  purely  mechanical,  inevitable  weeding  out  and  selecting 
by  Nature  (by  the  environmental  determining  of  what  may  and  what 
may  not  live)  through  uncounted  generations  in  unreckonable  time. 
This  is  Darwin's  causo-mechanical  theory  to  explain  the  transforma- 
tion of  species  and  the  infinite  variety  of  adaptive  modification.  A 
rigorous  automatic  Natural  Selection  is  the  essential  idea  in  Darwin- 
ism, at  least  in  Darwinism  as  it  is  held  by  the  present-day  followers 
of  Darwin. 

OBJECTIONS   TO   DARWINISM 

I.  Darwin  in  a  letter  to  his  friend  Hooker  (January  11,  1844) 
expresses  his  contempt  of  Lamarck's  ideas  in  the  following  words: 
''Heaven  defend  me  from  Lamarck's  nonsense  of  a  'tendency  to  pro- 
gression,' 'adaptations  from  the  slow  willing  of  animals,'  etc 

Lamarck's  work  appeared  to  me  to  be  extremely  poor;  I  got  not  a 
fact  or  idea  from  it." 

In  spite  of  these  views  Darwin's  Origin  of  Species  is  interlarded 
with  Lamarckian  explanations.  Whenever  the  author  feels  the  short- 
comings of  the  selection  factor  he  lapses  into  an  explanation  involving 
the  idea  that  the  effects  of  use  and  disuse  of  organs  are  inherited. 
Followers  of  Darwin,  especially  Weismann,  felt  this  to  be  the  chief 
defect  in  the  fabric  of  Darwinism  and  bent  their  efforts  chiefly  toward 
purging  Darwinism  of  all  taint  of  Lamarckism. 


248      READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

2.  Darwin  insisted  upon  the  idea  that  minute  fluctuating  varia- 
tions, which  we  now  know  are  to  a  large  extent  non-heritable,  were 
the  principal,  if  not  the  sole,  materials  for  natural  selection  to  work 
upon.  He  knew  of  a  considerable  number  of  "sports"  or  "saltatory 
variations"  (now  called  mutations),  but  considered  these  too  infre- 
quent to  furnish  the  necessary  basis  for  selection.  We  now  know 
that  mutations  may  be  as  small  as  fluctuating  variations  or  as  large 
as  "sports"  and  that  they  are  of  much  more  frequent  occurrence 
than  Darwin  supposed. 

3.  Darwin 'considered  all  variations  as  heritable.  He  did  not 
distinguish  between  somatic  variations  and  germinal  variations.  In 
fact,  as  we  learn  from  a  study  of  his  pangenesis  theory,  he  considered 
all  variations  as  in  the  first  instance  somatic,  and  subsequently 
transferred  by  means  of  gemmules  to  the  germ  cells.  Every  somatic 
variation,  whether  induced  by  use,  disuse,  in  response  to  environ- 
mental stimulus,  or  through  mere  spontaneous  variability,  was  sup- 
posed to  be  able  to  give  off  gemmules  into  the  blood  stream  that 
would  carry  to  the  germ  cells  the  physical  basis  of  the  varying  charac- 
ter. The  pangenesis  mechanism  is  now  known  to  have  no  basis 
in  fact. 

4.  The  natural-selection  theory  is  based  upon  a  mistaken  concep- 
tion of  the  methods  of  artificial  selection.  Darwin  believed,  without 
having  any  proof  for  this  belief,  that  the  way  in  which  domestic 
varieties  had  been  so  profoundly  modified  at  the  hands  of  man  was 
by  the  conscious  or  unconscious  selection  of  slight  fluctuating  varia- 
tions in  favorable  or  desired  directions,  and  that  this  resulted  in  the 
cumulative  improvement  or  enhancement  of  the  desired  characters 
over  a  long  series  of  generations.  Darwin  supposes  that  the  radically 
changed  conditions  of  domestication  hasten  and  stimulate  variability, 
thus  offering  a  better  opportunity  for  selection.  Transferring  this 
idea  to  nature,  he  thinks  that  changed  natural  conditions  stimulate 
variability,  just  as  does  domestication,  and  that  this  is  seized  upon  by 
natural  selection  to  make  for  adaptation  to  the  new  environment  and 
the  resultant  origin  of  new  species. 

Our  modern  experimental  studies  have  shown  that  somatic 
modifications  due  to  environmental  changes  are  not  hereditary,  and 
that  all  of  the  recent  domestic  varieties  whose  origin  has  been  observed 
have  been  the  result  of  suddenly  appearing  germinal  variations  or 
mutations,  that  arrive  fully  formed  and  cannot  be  improved  by  selec- 
tion, except  that  they  usually  need  to  be  selected  out  or  isolated  in 


CRITIQUE  OF  DARWINISM  249 

order   to   prevent    swamping   out    through    intercrossing   with    the 
parent-type. 

5.  Objection  has  frequently  been  made  to  Darwin's  idea  of  the 
purely  fortuitous  or  chance  character  of  variations.  According  to 
this  view  variations  occur  in  all  structures  and  in  all  directions  at 
haphazard,  so  that  there  would  be  the  widest  possible  opportunity  for 
a  given  adaptive  variation  to  occur  just  when  the  circumstances 
would  demand.  It  now  appears  that  variations  do  not  occur  in  all 
directions  in  random  fashion,  but  that  they  tend  to  follow  certain 
definite  paths  of  change;  in  other  words,  variations  are,  to  a  consider- 
able extent  at  least,  orthogenetic.  If  variations  really  tend  to  follow 
certain  definite  lines,  owing  to  purely  internal  causes,  natural  selection 
would  be  unnecessary,  at  least  until  orthogenesis  went  too  far  for  the 
good  of  the  species,  or  far  enough  to  be  of  real  importance  in  the 
struggle  for*  existence. 

6.  The  difficulty  of  explaining  how  natural  selection  could  make 
use  of  the  initial  stages  of  adaptive  structures  is  obvious.  It  is  incon- 
ceivable that  the  first,  almost  imperceptible  variation  in  a  favorable 
direction  could  be  of  selective  value,  so  as  to  effect  the  survival  of  the 
individual  or  the  relative  number  of  its  offspring.  What  would  be  the 
advantage  of  the  first  few  hairs  of  a  mammal  or  the  first  steps 
toward  feathers  in  a  bird  when  these  creatures  were  beginning  to 
diverge  from  their  reptilian  ancestors?  This  objection  is,  of  course, 
based  on  the  fluctuating-variation  idea.  If  the  mutation  idea  were 
substituted,  the  difficulty  would,  to  a  great  extent,  clear  up;  for  a 
mutation  might  be  of  sufficient  importance  in  one  generation  to  have 
selective  value  from  the  very  first. 

7.  Natural  selection  is  said  to  be  incapable  of  explaining  the  origin 
of  coadaptive  and  highly  complex  adaptations  whose  effectiveness 
depends  upon  the  perfection  of  their  adjustments  to  one  another.  For 
example,  we  may  refer  to  some  of  the  perfected  adaptations  described 
in  chapter  xiv.  In  the  case  of  the  electric  organs  of  certain  fish,  the 
-Darwinian  assumption  would  be  that  the  first  step  in  the  direction  of 
an  electric  organ  would  be  a  very  small  one,  and  that  it  was  built  up 
Httle  by  little  by  means  of  natural  selection.  But,  say  the  critics,  the 
electric  organ  would  be  of  no  value  until  it  became  powerful  enough 
to  impart  an  effective  shock  to  the  intruder,  and  this  would  not  be 
possible  if  the  character  began  in  a  small  way.  The  whole  phenome- 
non of  protective  resemblance  is  open  to  the  same  tyi^e  of  criticism. 
As  a  specific  example  of  this  we  may  cite  the  case  of  the  dried-leaf 


250     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

butterfly,  Kallima,  previously  described  (pp.  201,  202).  In  its  present 
condition  this  animal  has  a  strikingly  detailed  resemblance  to  a  dried 
leaf,  which  is  therefore  doubtless  of  some  value.  But  of  what  value 
would  be  the  first  tiny  change  in  the  direction  of  resemblance  ?  Until 
its  resemblance  became  close  enough  actually  to  deceive  the  enemies  of 
butterflies,  the  critics  claim,  there  would  be  no  chance  for  selection  to  act. 

8.  It  is  frequently  objected  that  a  vast  number  of  characters  of 
organs  are  useless  or  non-adaptive  and,  as  such,  could  not  have  arisen 
through  the  instrumentality  of  natural  selection.  If  these  useless 
characters,  which  are  sometimes  quite  large  and  prominent,  are 
independent  of  natural  selection,  why  do  we  need  natural  selection  to 
explain  adaptive  characters  ?  It  is  also  claimed  that  a  vast  number 
of  specific  peculiarities  are  useless  and  therefore  could  not  have  helped 
in  the  differentiation  of  species.  It  should  be  said  in  defense  that 
Darwin  realized  this  difficulty  quite  as  clearly  as  do  his  critics  and 
was  greatly  puzzled  by  it.  His  idea  of  correlated  variability,  however, 
helps  to  answer  it,  for  it  may  well  be  that  many  of  these  apparently 
useless  characters  are  correlated,  or  linked  in  inheritance,  with  charac- 
ters of  supreme  selective  value  such  as  general  hardiness  or  great 
fecundity.  Darwin  also  points  out  that  we  are  not  in  a  position  at* 
present  to  pronounce  judgment  on  the  value  of  many  structures  or 
functions  that  have  been  adjudged  non-adaptive. 

9.  Certain  characters  in  organisms,  past  and  present,  have  been 
interpreted  as  overspecializations,  organs  that  have  evolved  beyond 
the  range  of  usefulness  or  that  are  more  elaborate  than  is  demanded 
for  survival  under  the  conditions  of  life.  The  case  of  the  extinct  Irish 
elk  is  often  cited  as  an  example  of  overspecialization.  This  group  of 
animals  went  to  extremes  in  the  development  of  size  and  elaboration 
of  horns  far  beyond  the  range  of  usefulness,  so  that  it  is  said  to  have 
brought  about  the  extinction  of  the  race.  Natural  selection,  which  is 
supposed  to  have  brought  the  horns  up  to  the  point  of  adaptive 
perfection,  should  have  kept  them  within  the  bounds  of  usefulness. 

Again,  the  enormously  overgrown  and  overspecialized  dinosaurs 
of  long  ago  are  thought  of  as  having  followed  their  lines  of  evolution 
far  beyond  the  point  of  greatest  effectiveness  and  adaptability. 

10.  The  rudimentation  of  structures,  which  is  such  a  common 
phenomenon  in  nature,  is  said  to  meet  with  no  adequate  explanation 
on  a  selection  basis.  The  case  of  the  whale's  vestigial  hind  limbs  is 
a  case  in  point.  Darwin's  explanation  would  be  that  under  aquatic 
conditions  the  first  whale  ancestors  would  be  handicapped  by  hind 


CRITIQUE  OF  DARWINISM  251 

legs  and  that  any  decrease  in  their  size,  which  would  be  enhanced  by 
disuse,  would  be  of  advantage.  This  might  seem  reasonable  during 
the  main  period  of  hmb  reduction,  but,  after  the  limb  is  reduced  to  a 
subcutaneous  rudiment,  there  could  be  Uttle  advantage  in  carrying 
the  rudimentation  still  farther.  Some  whales  have  the  hind  Hmbs 
much  more  profoundly  reduced  than  others,  although  they  are  all 
thoroughly  out  of  the  way  and  involve  no  hindrance  in  swimming. 
Any  number  of  similar  cases  of  the  same  kind  might  be  cited.  Darwin 
had  no  explanation  to  offer  except  a  resort  to  Lamarckism;  but 
Weismann,  the  ablest  neo-Darwinian,  offered  the  theory  of  panmixia 
to  cover  this  objection,  a  theory  which  is  mentioned  in  chapter  i  and 
will  be  discussed  later. 

11.  It  is  objected  that,  unless  favorable  variations  occur  in  a  large 
number  of  individuals  at  the  same  time,  the  character  would  be 
swamped  out  by  intercrossing  with  individuals  not  possessing  the 
favorable  variation.  The  probability  that  such  a  swamping-out 
would  occur  was  shown  mathematically  by  various  critics.  By  way 
of  answer  to  this  objection  there  arose  a  number  of  ''isolation  theo- 
ries," according  to  which  favorably  varying  individuals  would  be 
protected  from  back-crossing  with  the  non-varying  individuals.  We 
might  also  point  out  that  the  Mendelian  laws  of  dominance  and 
segregation  would  serve  to  prevent  loss  of  any  new  favorable  character. 

12.  It  is  objected  that  natural  selection  might  explain  the  ''sur- 
vival, but  not  the  arrival,  of  the  fittest."  But  Darwin  met  this 
perfectly  when  he  said:  ''Some  have  even  imagined  that  natural 
selection  induces  variability,  whereas  it  implies  only  the  preservation 
of  such  variations  as  arise  and  are  beneficial  to  the  being  under  its 
conditions  of  life." 

13.  Criticism  has  been  directed  against  natural  selection  because 
of  the  fact  that  some  of  thje  supporters  of  Darwinism,  notably  Weis- 
mann, have  made  the  claim  that  natural  selection  is  the  sole  cause  of 
evolution.  This  idea  of  the  Allmacht  or  all-sufhciency  of  natural 
selection  was  not  Darwin's,  as  is  clear  from  the  following  statement: 
"I  am  convinced  that  natural  selection  has  been  the  most  important, 
but  not  the  exclusive  means  of  modification." 

14.  It  is  objected  that  many,  if  not  most,  of  the  fluctuating  varia- 
tions with  which  Darwinism  deals  are  purely  quantitative  or  plus- 
and-minus  variations;  whereas  the  differences  between  species  are 
quahtative.  This  is  a  serious  objection  and  difficult  to  meet,  yet  a 
fair  defense  has  been  formulated  by  leading  neo-Darwinians. 


252     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

15.  There  is  a  growing  skepticism  on  the  part  of  biologists  as  to 
the  extreme  fierceness  of  the  struggle  for  existence  and  of  the  conse- 
quent rigor  of  selection.  It  may  be  answered  that  no  very  obvious 
fierceness  is  implied  in  the  theory.  So  long  as  overproduction  and  a 
shortage  of  space  and  food  exists  the  struggle  for  existence  is  inevitable. 

16.  Special  objections  are  offered  to  the  subsidiary  theory  of 
sexual  selection.  It  is  said  that  the  type  of  sexual  selection  involving 
active  rivalry  and  battling  for  mates  needs  no  special  theory,  inasmuch, 
as  this  is  a  mere  phase  of  the  struggle  for  the  maintenance  of  the  full 
life,  including  the  chance  to  leave  offspring.  It  is  against  the  other 
side  of  sexual  selection,  which  involves  passivity  on  the  part  of  the 
male  and  active  choice  on  the  part  of  the  female  of  the  more  beautiful 
or  otherwise  attractive  male,  that  objection  is  raised.  It  is  claimed 
that  such  choice  implies  too  high  aesthetic  powers  in  animals  of 
relatively  poor  vision  and  mentality.  Experiments  have  been  per- 
formed with  moths,  in  which  the  male  and  female  coloration  is 
strikingly  different,  in  order  to  determine  whether  females  actually 
do  exercise  any  choice  of  mates  that  is  based  on  considerations  of 
appearance.  The  result  proved  conclusively  that  color  patterns  have 
no  value  in  mating,  but  that  the  female  is  passive  and  mates  with  the 
first  male  to  present  himself,  while  the  male  finds  the  female  through 
his  exquisitely  effective  sense  of  smell. 

We  know  now,  however,  that  secondary  sexual  characters  are 
intimately  bound  up  in  a  physiological  way  with  the  functioning  of 
the  sex  glands  and  are  therefore  doubtless  to  be  interpreted  as  mere 
non-adaptive  correlative  variations  that  need  no  special  evolutionary 
explanation. 

DEFENSE    OF   DARWINISM 

In  presenting  these  sixteen  objections,  we  have  in  most  cases 
indicated  the  lines  upon  which  the  objections  have  been  met,  if  they 
have  been  met.  Not  all  of  these  objections  are  considered  serious  at 
the  present  time,  for  some  are  based  upon  lack  of  a  full  knowledge  of 
what  Darwin  actually  wrote;  others  are  largely  academic  in  character 
and  fail  to  stand  up  under  actual  test;  still  others  have  been  more  or 
less  adequately  met  by  subsidiary  or  supporting  theories  which  have 
been  advanced  by  various  neo-Darwinians. 

Most  of  the  special  objections  raised  in  this  chapter  have  received 
the  attention  of  various  able  Darwinians,  and  the  student  of  evolution 
would  doubtless  be  interested  in  the  expert  and  fair-minded  defense 


CRITIQUE  OF  DARWlxMSM 


■56 


of  Darwinism  at  the  hands  of  Professor  V.  L.  Kellogg  as  it  appears  in 
his  book  Darwinism  To-Day. 

A  much  briefer  and  considerably  more  general  defense  is  that  of 
J.  L.  Tayler,  which  is  as  follows: 

GENERAL  DEFENSE    OF   DARWINISM^ 
J.    L.    TAYLER 

To  realise  how  far  the  theory  of  selection  is  capable  of  explaining 
the  facts  of  organic  evolution,  it  is  necessary  to  bear  in  mind  the 
postulates  in  which  the  theory  is  founded. 

1.  It  is  obvious  that  natural  selection  can  only  act  by  preserv- 
ing or  eliminating  the  complete  organism.  Selection  must  therefore 
be  organismal.  This  Darwin  and  other  selectionists  have  clearly 
recognised. 

2.  As  the  whole  organism  must  survive,  if  the  favourable  variation 
or  variations  are  to  be  preserved,  it  follows  that  certain  minor  un- 
favourable variations  may  also  be  preserved  if  they  happen  to  exist 
in  an  individual  which  survives  on  account  of  its  major  favourable 
variations.  And  since  no  individual  is  completely  adapted  to  its 
environment,  it  follows  that  there  must  be  always  a  variable  amount 
of  residual  unfavourable  variability  in  every  organism. 

3.  This  residual  unfavourable  variability  may  be  of  considerable 
utility  under  changed  conditions. 

4.  Complementary  specialisation  of  parts,  as  Spencer  has  shown, 
is  favourable  to  successful  competition,  and  as  it  is  the  whole  organism 
that  is  selected  or  eliminated,  it  follows  that  any  weakness  of  one 
specialised  part,  since  it  would  disturb  the  balance  of  all,  would  be 
detrimental.  The  more  complex  the  organism,  the  more  specialised 
the  structures,  the  more  dependent  one  part  will  be  on  the  others  for 
its  existence,  hence  a  complementary  specialising  tendency  will  be 
favoured  by  selection,  and  therefore  all  struggles  of  one  part  of  an 
organism  with  another  will  be  reduced  to  a  minimum. 

It  is  clear  that  there  must  be  some  underlying  criterion  which 
determines  whether  any  given  organism  shall  be  selected  or  not,  and 
that  criterion  must  be  the  net  result  of  its  adaptability  to  its  environ- 
ment. One  organism  may  conceivably  survive,  by  its  possession  of 
a  large  number  of  small  favourable  variations,  while  another  may 
survive  in  virtue  of  a  single  valuable  one,  but  in  each  case  it  would  be 

^  From  J.  L.  Tayler,  "The  Scope  of  Natural  Selection,"  Naturd  Scieme,  1899. 


254     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

the  whole  value  of  that  organism  which  determined  its  survival. 
This  fact  is  continually  disregarded  by  opponents  of  the  neo-Darwinian 
position,  yet  this  selection  of  the  organism  as  a  whole  is  the 
fundamental  postulate  from  which  the  theory  of  selection  starts. 
Thus  it  is  not  uncom.mom  to  read  criticisms  bearing  on  the  early 
development  of  some  organ,  in  which  the  inadequacy  of  selection  is 
supposed  to  be  proved  by  the  writer  demonstrating,  or  believing  he 
has  demonstrated,  the  fact  that  the  particular  variation  in  question 
must  have  been  too  small  to  be  by  itself  of  selection  value.  In  many 
cases  the  particular  variation  would,  no  doubt,  if  taken  alone  be,  as 
the  objector  asserts,  too  unimportant  to  be  selected,  but  as  it  is  the 
whole  organism  that  is  selected,  it  is  not  logical  to  make  an  artificial 
separation  and  study  the  development  of  one  organ  or  structure 
irrespective  of  the  other  organs  with  which  it  is  in  nature  associated. 
Every  organ  in  its  evolution  must  he  considered  in  relation  to  the  whole 
of  the  particular  orga^iism  in  which  that  particular  stage  of  development 
of  that  organ  is  found. 

Starting,  therefore,  with  this  fact  that  the  net  value  of  adaptability 
of  the  whole  organism  to  its  environment  must  be  the  basis  which 
determines  selection  or  elimination,  it  will  follow  that  certain  lines  of 
development  will  result  from  the  application  of  this  criterion.  In  a 
series  of  organisms  placed  under  new  conditions,  elimination  will 
proceed  along  lines  essential  to  bring  about  a  proper  adjustment  to 
the  new  conditions.  If  the  offspring  of  these  adjusted  organisms 
merely  repeated  in  their  generation  the  characters  of  the  exterminated 
as  well  as  of  the  surviving  organisms,  that  temporary  adjustment 
would  be  permanent  as  long  as  the  conditions  were  unchanged.  But 
since  the  offspring  are  produced  only  by  the  surviving  organisms, 
selection  is  continually  raised  to  higher  and  higher  planes  of  adapta- 
tion, and,  therefore,  as  long  as  conditions  remain  constant,  the 
tendency  of  selection  must  be,  as  Darwin  clearly  saw,  cumulative. 
He  did  not,  however,  apparently  see  that  from  this  cumulative 
tendency  definite  variability  must  arise  out  of  indefinite. 

Selection  in  direct  relation  to  climatic  conditions  is,  therefore,  of 
very  minor  importance,  while  selection  among  the  members  of  a 
species  and  all  forms  of  inter-organismal  selection  is  of  infinitely  more 
importance,  since  it  is  this  interaction,  produced  by  the  offspring  in 
different  degrees  inheriting  the  advantages  of  both  parents  (both  of 
whom  have  survived  on  account  of  certain  advantages),  that  leads  to 
the  cumulative  development  and  never-ending  struggle  for  survival. 


CRITIQUE  OF  DARWINISM  255 

Darwin  came  very  near  to  this  conception  of  definite  variability  when 
he  pointed  out  that  "if  a  country  were  changing,  the  altered  conditions 
would  tend  to  cause  variation,  not  but  what  I  believe  most  beings 
vary  at  all  times  enough  for  selection  to  act  on."  Extermination 
would  expose  the  remainder  to  the  "mutual  action  of  a  different  set  of 
inhabitants,  which  I  believe  to  be  more  important  to  the  life  of  each 
being  than  mere  climate,"  and  as  "the  same  spot  will  support  more 
life  if  occupied  by  very  diverse  forms,"  it  is  evident  that  selection 
will  favour  very  great  diversity  of  structure. 

Bearing  in  mind  this  cumulative  action  of  selection  it  will  follow 
that  under  constant  or  relatively  constant  conditions  the  struggle  for 
successful  living  will  become  more  and  more  selective  in  character, 
even  if  the  actual  number  of  inhabitants  remain  more  or  less  the  same 
as  when  the  struggle  first  commenced.  The  selection  of  variations 
will  thus  tend  to  pass  through  certain  more  or  less  ill-defined,  but 
nevertheless,  real  stages.  In  proportion  as  the  struggle  becomes 
intense,  either  from  the  number  or  from  the  increasing  adaptability 
of  the  organisms,  or  both,  certain  major  essential  adaptations,  which 
were  necessary  for  the  climatic  and  other  more  or  less  comparativelv 
simple  conditions,  will  be  supplemented  by  minor  auxiliary  variations 
which  in  the  earlier  stages  would  not  have  appeared.  And  still  later, 
as  more  and  more  rigorous  conditions  of  life  were  imposed,  the  advan- 
tage would  tend  to  rest  with  those  organisms  which  possessed  highly 
co-ordinated  adaptations,  since  this  would  entail  more  rapid  respon- 
siveness to  environment. 

As  evolution  advances  from  the  unspecialised  to  the  specialised, 
and  higher  and  higher  forms  of  life  come  into  being,  with  increasing 
complexity  and  specialisation  of  parts  entailing  an  increasingly  delicate 
adjustment  of  those  parts  to  each  other's  needs,  the  relation  of  each 
part  to  the  whole  organism  becomes  of  more  and  more  importance, 
and  it  follows  that  selection  must  become  more  and  more  generalised 
in  its  action.  No  single  variation  could  be  of  service  to  any  of  the 
higher  forms  of  life  unless  it  was  in  more  or  less  complete  harmony 
with  the  whole  tendency  of  the  individual.  The  adjustment  of  parts 
and  their  mutual  interdependence  make  it  essential  for  adaptation 
that  the  relation  of  parts  be  preserved;  consequently,  correlated 
minute  favourable  variations  will  tend  to  be  more  and  more  selected 
as  evolution  passes  from  the  unspecialised  to  the  specialised  forms  of 
life.  This  response  of  the  whole  organism  should  be  still  more  delicate 
in  those  forms  of  life  that  are  continually  subjecting  themselves  to 


256      READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

changed  conditions;  hence  this  delicacy  of  adjustment  is  far  more 
necessary  in  the  higher  forms  of  animal  hfe  than  in  more  stationary 
plant  organisms,  and  in  the  developing  nervous  systems  of  animals  we 
have  just  the  central  adjusting  system  that  is  required  for  these  condi- 
tions. With  evolution  of  type  there  will  thus  be  an  increasingly  definite 
tendency  given  to  organic,  especially  the  animal,  forms  of  life,  if  the 
acting  principle  of  evolution  has  been  selectional.  Selection  is,  therefore, 
able  to  account  for  the  steadily  progressive  tendency  of  life  as  a  whole 
without  calling  to  its  aid  any  unknown  and  doubtful  perfecting  principle. 
To  summarise:  Natural  selection,  acting  on  the  whole  organism, 
tends  to  produce  more  and  more  definite  tendencies  in  all  surviving 
forms  of  life,  which  tendencies  are  progressive  and  continuous  in  char- 
acter. Variable  conditions,  by  partially  altering  the  line  of  selection, 
induce  a  temporary  indefiniteness.  And  lastly,  the  process  of  selec- 
tion being  itself  able  to  be  the  indirect,  though  not  the  direct,  cause 
of  those  favourable  variations,  which  it  subsequently  selects  from,  is 
able  to  dispense  with  any  subsidiary  factors,  provided  it  has  a  certain 
number  of  elementary  properties  of  life  which  afford  sufficient  material 
to  work  with. 


EXPERIMENTAL   SUPPORT   OF   THE   EFFECTIVENESS 
OF   NATURAL   SELECTION 

Weldon's  experiments  with  the  shore-crabs  of  Plymouth  Sound. — 
These  experiments  seem  to  show  that  under  changed  environmental 
conditions  natural  selection  acts  upon  minute  fluctuating  variations 
of  linear  or  quantitative  type  so  as  to  produce  an  alteration  in  the 
species;  exactly  as  Darwinism  would  hold.  A  large  breakwater  was 
so  placed  near  the  mouth  of  Plymouth  Sound  that  the  rate  of  flow  of 
the  river  water  was  greatly  slowed  down  in  certain  regions.  This 
allowed  an  increased  settling  of  the  fine  china-clay  sediment  that  is 
carried  by  the  river,  and  the  changed  condition  caused  the  death  of 
numerous  crabs  of  the  species  Carcinus  maenas.  The  question  arose 
as  to  whether  the  survivors  and  those  that  had  perished  showed  any 
consistent  differences  on  the  basis  of  which  selection  could  be  operat- 
ing. Careful  measurements  of  hundreds  of  individuals  showed  that 
the  mean  breadth  of  frontum  is  slightly  less  in  the  survivors  than  in 
the  perished.  Measurements  were  repeated  in  two  subsequent  years 
and  it  was  found  that  there  was  a  progressive  narrowing  of  the 
frontum.     As  an  experimental  check  upon  these  conclusions  Weldon 


CRITIQUE  OF  DARWINISM  257 

placed  a  number  of  crabs  in  a  large  aquarium,  in  which  china-clay  was 
kept  partly  in  suspension,  and  found  that  about  half  of  them  died. 
Again  the  survivors  were  compared  statistically  with  the  perished  and 
the  same  relation  was  found  to  hold :  that  the  survivors  had  a  mean 
frontal  breadth  distinctly  narrower  than  that  of  the  perished.  W'el- 
don  concludes  that  his  experiments  ''have  demonstrated  two  facts 
about  these  crabs;  the  first  that  their  mean  frontal  breadth  is  dimin- 
ishing year  by  year  at  a  measurable  rate,  which  is  more  rapid  in  males 
than  in  females;  the  second  is  that  this  diminution  in  frontal  breadth 
occurs  in  the  presence  of  a  material,  namely,  fine  mud,  which  is 
increasing  in  amount,  and  which  can  be  shown  experimentally  to 
destroy  broad-fronted  crabs  at  a  greater  rate  than  crabs  with  narrower 
frontal  margins  ....  and  I  see  no  escape  from  the  conclusion 
that  we  have  here  a  case  of  Natural  Selection  acting  with  great 
rapidity,  because  of  the  rapidity  with  which  the  conditions  of  life 
are  changing." 

Cesnola's  experiments  with  Mantis. — ^To  test  the  selective  value 
of  color  markings  Cesnola  fixed  specimens  of  the  brown  and  green 
Mantis  religiosa  on  plants,  some  of  which  were  against  harmonious, 
others  against  disharmonious  backgrounds.  The  result  was  that  most 
of  those  which  were  inconspicuous  because  of  a  harmonious  back- 
ground escaped,  while  most  of  the  others  were  eaten  up  by  birds. 

Poulton's  and  Sanders'  experiments  with  butterfly  pupae. — 
Numerous  pupae  of  various  colors  were  placed  under  conditions  favor- 
ing protective  coloration  and  others  under  opposite  conditions.  The 
conclusion  was  that  protective  coloration  is  a  real  survival  factor,  and 
one  that  operates  so  as  to  give  the  protectively  colored  individual 
a  decided  advantage  in  the  struggle  for  existence. 

Davenport's  experiments  with  chickens. — A  number  of  chickens, 
some  black,  some  white,  and  some  barred  or  checkered  in  color,  were 
allowed  to  wander  free  in  the  fields.  Hawks  killed  most  of  the  whites 
and  many  of  the  blacks,  but  spared,  to  a  large  extent,  the  less  con- 
spicuous checkered  and  barred  types  which  are  harder  to  detect 
against  a  mixed  background. 

All  of  these  experiments  merely  tend  to  show  that  discriminate 
survival  actually  occurs,  but  only  the  experiment  of  Weldon  has  a 
bearing  on  the  possibility  that  mere  quantitative  changes  of  small 
dimensions  might  under  certain  conditions  be  of  selective  value.  We 
badly  need  more  experimental  evidence  of  this  sort  and  until  this 
is  forthcoming  we   shall  have   to  admit   that   there  is  very  little 


258     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

experimental  evidence  in  favor  of  the  type  of  natural  selection  that 
Darwin  stood  for. 

THE   PRESENT   STATUS   OF   NATURAL   SELECTION 

It  has  come  to  be  rather  generally  believed  that  the  natural 
selection  that  Darwin  himself  believed  in  stands  almost  unscathed  as 
one  very  important  causal  factor.  In  fact  it  is  the  only  explanation 
ever  offered  for  adaptation  that  even  approaches  adequacy.  As  an 
explanation  of  the  origin  of  new  types  or  new  species  it  falls  far  short 
of  adequacy,  and  I  think  Darwin  evidently  realized  this,  a?lthough  he 
was  unfortunate  enough  to  entitle  his  book  Origin  of  Species.  As 
an  explanation  of  the  origin  and  perfection  of  adaptation  natural 
selection  has  only  one  rival,  the  far  less  satisfactory  Lamarckian  theory 
of  the  inheritance  of  acquired  characters.  There  is  a  strong  tendency 
among  geneticists  to  conclude  that  the  modern  germ-plasm  hypothe- 
sis, with  the  aid  of  mutations  and  the  mechanism  of  Mendelian  inherit- 
ance, furnishes  all  the  necessary  explanation  of  the  causes  of  evolution. 
There  is,  however,  marked  dissent  to  this  extreme  position.  In  his 
critique  of  De  Vries's  rather  extreme  position  that  the  mutation 
theory  needs  no  aid  from  natural  selection,  Weismann  shows  in  most 
able  fashion  the  inadequacy  of  mutations  to  account  for  adaptation, 
and,  in  contrast,  how  well  natural  selection  accounts  for  them. 

In  a  very  recent  paper  Professor  C.  C.  Nutting  attempts  to  show 
that  natural  selection  is  still  an  important  factor  in  evolution  and  quite 
in  harmony  with  both  the  mutation  theory  and  Mendelism.  We 
perhaps  can  close  the  present  chapter  no  more  fittingly  than  by 
quoting  Professor  Nutting's  paper. 


THE   RELATION   OF   MENDELISM  AND   THE   MUTATION   THEORY 

TO   NATURAL   SELECTION^ 

C.   C.   NUTTING 

Two  marked  tendencies  are  evident  in  the  history  of  any  important 
theory  after  its  publication. 

First.  The  followers  of  the  discoverer  carry  the  theory  too  far 
and  attempt  too  universal  an  application.  This  is  manifestly  true 
of  Wallace  and  Weismann  who  out-Darwined  Darwin  in  their  claims 
for  natural  selection;  of  the  followers  of  Mendel,  such  as  Morgan  and 

''  From  an  address  given  before  the  Genetics  branch  of  the  American  Associa- 
tion for  the  Advancement  of  Science,  December,  1920;  Science^  N.S.,  Vol.  LIII. 


CRITIQUE  OF  DARWINISM  259 

Pearl;   and  of  many  mutationists  who  make  much  greater  claims  for 
that  theory  than  does  De  Vries  himself. 

Second.  Each  generation  of  biologists  is  so  occupied  with  its  own 
work  and  contemporary  theories  that  it  makes  no  real  effort  to 
understand  preceding  theories. 

This  second  tendency  seems  to  me  most  marked  in  the  attitude  of 
present  workers  along  genetic  lines  towards  natural  selection.  They 
reveal  an  apparent  lack  of  understanding  of  what  Darwin  really  meant 
and  of  what  he  claimed;  and  when  criticising  that  theory  they  are 
often  engaged  in  the  classic,  but  unprofitable,  exercise  of  ''fighting 
windmills." 

In  view  of  these  facts  I  hope  you  will  pardon  me  if  I  present  in  as 
few  words  as  possible  just  what  I  believe  to  be  the  main  factors  which 
Darwin  presented  as  resulting,  in  their  actions  and  reactions,  in 
natural  selection.     These  factors  are  three  in  number: 

First.  Heredity,  by  which  the  progeny  tend  to  resemble  their 
parents  more  than  they  do  other  individuals  of  the  same  species. 

Second.  Individual  variation,  by  which  the  progeny  tend  to 
depart  from  the  parental  type  and  sometimes  from  the  specific  tvpe. 

Third.  Geometrical  ratio  of  increase,  by  which  each  species  tends 
to  produce  more  individuals  than  can  survive. 

Each  of  these  factors  is  practically  axiomatic,  so  little  is  it  open 
to  argument. 

No  one  doubts  the  fact  of  heredity,  whether  pangenesis,  Weis- 
mannism  or  Mendelism  be  the  correct  expression  of  the  mechanism 
involved.  These  do  not  affect  the  fact  of  heredity  nor  invalidate  it 
as  a  factor  in  natural  selection. 

No  one  doubts  the  fact  of  variation;  whether  it  is  the  ''  individual 
variation"  of  Darwin,  the  "fluctuating  variety"  or  the  "mutation" 
of  De  Vries.  All  that  is  necessary  for  Darwin's  purpose  is  that  there 
be  heritable  variations.  That  there  are  such  things  all  parties  agree 
and  it  matters  httle  what  you  call  them.  They  are  adequate  to  act 
as  a  factor  in  the  Darwinian  scheme. 

No  one  doubts  the  fact  of  geometrical  ratio  of  increase.  It  is  a 
proposition  easily  capable  of  mathematical  demonstration,  and  that 
is  sufficient  for  Darwin's  purpose. 

These  three  factors,  then,  are  not  debatable  as  facts,  whatever 
their  mechanism  or  causes. 

A  moment's  reflection  will  show  that  geometrical  ratio  of  increase 
is  a  quantitative  factor,  giving  an  abundance  lof   individuals  from 


26o     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

which  to  select ;  that  individual  variation  is  a  qualitative  factor,  giving 
the  differences  which  make  a  selection  possible;  and  that  heredity  is 
a  conservative  factor,  holding  fast  those  characters  which  better  fit 
the  organism  to  its  environment. 

Now  it  seems  to  me  that  there  is  no  possible  outcome  of  the 
necessary  action  and  interaction  of  these  three  factors  that  would 
not  be  a  selection  of  some  sort.  Darwin  thought  it  comparable  in  a 
large  way  to  the  selection  by  which  the  stock-breeder  improves  his 
herd,  and  therefore  called  it  ''natural  selection,"  carefully  guarding 
the  phrase  from  misinterpretation  from  the  teleological  angle  as  well 
as  from  a  too  close  parallelism  between  artificial  and  natural  selection. 
And  I  believe  no  one  has  suggested  a  more  acceptable  term  for  the 
process  of  selection  resulting  from  the  interplay  of  natural  laws. 

Three  outstanding  theories  have  been  advanced  since  the  publica- 
tion of  the  Origin,  each  involving  an  advance  in  our  knowledge  of 
the  mechanism  of  heredity  on  the  one  hand  and  the  origin  of  varia- 
tions on  the  other. 

Weismann's  theory  of  the  continuity  and  stability  of  the  germ 
plasm  was  of  immense  importance  in  its  discussion  of  the  mechanism 
of  heredity,  and  his  amphimixis  gave  a  plausible  explanation  of  the 
origin  of  variations.  His  results  were  almost  universally  regarded  as 
confirming  and  greatly  extending  the  scope  of  natural  selection. 

Mendel's  theory  regarding  the  purity  of  the  gametes,  their  segre- 
gation in  the  sex  cells,  and  the  whole  complex  Mendelian  mechanism 
so  admirably  described  by  Morgan;  all  of  these,  fascinating  and 
important  as  they  are,  deal  with  the  mechanism  rather  than  the  fact 
of  heredity.  In  my  opinion  their  acceptance  or  rejection  does  not 
affect  the  status  of  natural  selection  as  a  theory  of  organic  evolution. 

But  it  is  the  theory  of  mutation  that  has  furnished  most  of  the 
ammunition  for  the  opponents  of  natural  selection;  and  this  in  spite 
of  the  fact  that  De  Vries,  the  originator  of  the  mutation  theory, 
expresses  himself  with  great  clarity  as  follows: 

"  My  work  claims  to  be  in  full  accord  with  the  principles  laid  down 
by  Darwin  and  to  give  a  thorough  and  sharp  analysis  to  some  of  the 
ideas  of  variability,  inheritance,  selection,  and  mutation  which  were 
necessarily  vague  in  his  time." 

In  1904,  when  these  words  were  published,  there  did  seem  to  be 
a  sharp  distinction  between  the  ideas  of  Darwin  and  those  of  De  Vries. 
The  former  believed  that  natural  selection  acted  upon  many  small 
variations  and  accumulated  them  until  the  differences  were  sufficient 


CRlTIQtlf:  OV  bARWINISAt  261 

to  constitute  new  species;  while  De  Vries  claimed  that  new  species 
were  formed  by  the  sudden  appearance  by  mutations  of  forms  specifi- 
cally distinct  from  the  parents.     That  mutants  were  new  species! 

It  seems  evident  that  Darwin  did  not  regard  "  saltatory  evolution  " 
as  the  common  method,  while  De  Vries  did. 

Darwin  believed  that  individual,  usually  small,  variations  fur- 
nished the  material  on  which  selection  acts;  while  De  Vries  thought 
that  mutants,  usually  large  variations,  furnished  the  material.  Both, 
however,  believed  thoroughly  that  natural  selection  was  a  vera  causa  of 
evolution. 

But  things  have  changed  greatly  since  1904.  The  work  of 
Morgan,  Castle,  Jennings  and  a  host  of  others  has  shown  that  many 
mutations  are  so  small,  from  a  phenotypic  standpoint,  that  they  are 
quantitatively  no  greater  than  the  individual  variations  of  Darwin; 
and  that  they  are'  heritable  in  the  Mendelian  way. 

Castle  produced  a  perfectly  graded  series  of  hooded  rats  which 
exhibits  almost  ideally  the  steps  by  which  a  new  form  might  be 
produced  by  natural  selection.     He  says: 

"If  artificial  selection  can,  in  the  brief  span  of  a  man's  lifetime, 
mould  a  character  steadily  in  a  particular  direction,  why  may  not 
natural  selection  in  unlimited  time  also  cause  progressive  evolution  in 
directions  useful  to  the  organism  ?" 

Jennings  says: 

''Sufficiently  thorough  study  shows  that  minute  heritable  v-aria- 
tions — so  minute  as  to  represent  practically  continuous  gradations — 
occur  in  many  organisms:    some  reproducing  from  a  single  parent, 

others  by  biparental  reproduction It  is  not  established  that 

heritable  changes  must  be  sudden  large  steps;  while  these  may  occur, 
minute  heritable  changes  are  more  frequent.  Evolution  according  to 
the  typical  Darwinian  scheme,  through  the  occurrence  of  many  small 
variations  and  their  guidance  by  natural  selection,  is  perfectly  con- 
sistent with  what  experimental  and  paleontological  studies  show  us; 
to  me  it  appears  more  consistent  with  the  data  than  does  any  other 
theory." 

Many  believers  in  mutation  have  been  needlessly  befuddled  by 
the  diverse  meanings  of  "variations"  as  used  by  Darwin  and 
De  Vries.  Darwin  included  in  his  "individual  variations"  both  the 
^'fluctuating  varieties"  and  the  "mutations"  of  De  Vries.  Pheno- 
typically  they  cannot  even  now  be  distinguished.  De  \'rics  himself 
candidly  admits  that  this  was  Darwin's  attitude,  thus  proving  himself 


262     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

more  clear-sighted  than  many  of  his  followers.  All  that  Darwin 
needed  for  his  purpose  was  proof  of  variations  that  are  heritable,  and 
these  are  found  in  mutations,  be  they  large  or  small. 

Just  as  Mendelism  has  to  do  with  the  mechanism  and  not  the  fact 
of  heredity,  so  the  mutation  theory  deals  with  the  nature  and  not  the 
fact  of  variations.  Neither,  in  my  opinion,  has  any  implication  that 
is  antagonistic  to  the  theory  of  natural  selection. 

The  statement  has  been  made  that  natural  .selection  "originates 
nothing"  because  it  does  not  explain  the  origin  of  variations.  I 
must  confess  scant  patience  with  this  point  of  view.  As  well  say 
that  the  sculptor  does  not  make  the  statue  because  he  does  not 
manufacture  the  marble  or  his  chisel;  or  that  the  worker  in  mosaic 
originates  nothing  because  he  does  not  make  the  bits  of  stone  which 
he  assembles  in  his  design! 

The  material  corresponding  to  the  bits  of  stone"  in  the  mosaic  is 
furnished  by  heredity  and  variation,  and  its  quantity  by  geometrical 
ratio  of  increase.  Natural  selection  acts  in  selecting  and  putting 
together  this  material  in  the  formation  of  new  species.  Thus,  in  a 
true  sense,  it  seems  evident  that  something  new  has  appeared — 
something  that  is,  but  was  not. 

Another  favorite  figure,  introduced  I  believe  by  De  Vries,  is 
"Natural  selection  acts  only  as  a  sieve"  determining  which  forms 
shall  be  retained  and  which  shall  be  discarded.  This  also  seems  to 
me  to  fall  short  of  a  complete  statement  of  the  truth.  If  the  material 
subjected  to  the  sifting  process  be  regarded  as  changing  with  each 
generation  by  the  addition  of  variations,  or  mutations  if  you  prefer, 
some  of  which  are  favorable  to  a  nicer  adjustment  of  the  species  to  its 
environment,  the  figure  would  be  more  nearly  correct.  To  make  it 
complete,  however,  the  mesh  of  the  sieve  must  change  from  generation 
to  generation  so  that  a  quantitative  variation  which  would  be  preserved 
in  one  generation  would  be  discarded  in  a  later  one.  But  in  this  case 
natural  selection  would  do  more  than  a  sieve  could  do.  It  would 
combine  a  number  of  favorable  variations  in  the  production  of 
something  new,  a  new  species! 

In  conclusion  it  seems  to  me  that  we  are  justified  in  maintaining 
that  Mendelism  and  the  mutation  theory,  while  forming  the  basis  of 
the  most  brilliant  and  important  advances  in  biological  knowledge  of 
the  last  half-century,  have  neither  weakened  nor  supplanted  the 
Darwinian  conception  of  the  "Origin  of  species  by  means  of  Natural 
Selection." 


CHAPTER  XVIII 
OTHER  THEORIES  OF  SPECIES-FORAHNG 

H.  H.   N. 
THEORIES   AUXILIARY   TO   NATURAL   SELECTION 

The  post-Darwinian  causo-mechanical  theories  fall  quite  naturally 
into  two  categories:  those  that  were  devised  by  Darwinians  to  bolster 
up  natural  selection  and  to  free  it  of  some  of  its  most  obvious  objec- 
tions, while  retaining  the  essential  features  of  the  principle;  and  those 
that  were  meant  to  be  substitutes  for  and  therefore  quite  opposed  to 
natural  selection.  The  former  theories  have  been  classed  as  auxiliary, 
and  the  latter  as  alternative  theories  to  natural  selection. 

The  several  theories  of  Weismann  will  be  dealt  with  first  as  the 
most  important  of  the  purely  auxihary  theories.  ''Panmixia"  is 
designed  to  explain,  without  recourse  to  Lamarckism  and  in  harmon\' 
v/ith  natural  selection,  the  degeneration  or  atrophy  of  organs  which 
seemed  to  be  inadequately  explained  by  Darwin.  "Germinal  Selec- 
tion" is  supposed  to  explain  the  initial  stages  of  adaptations  and 
allied  phenomena,  and  thus  to  aid  natural  selection  at  one  of  its 
weakest  points. 

weismann's  theory  of  panmixia 

The  following  statement  of  "panmixia, "  as  given  by  S.  Herbert,  is 
concise  and  to  the  point: 

"Cessation  of  selection  as  a  cause  of  atrophy  was  first  proposed 
by  Romanes.  Later  on,  Weismann,  whilst  examining  the  validity  of 
the  principle  of  use-inheritance,  adopted  the  same  idea,  called  by  him 
'panmixia,'  in  order  to  account  for  the  dwindling  and  disappearance 
of  useless  organs  without  having  recourse  to  the  Lamarckian  factors. 
If  natural  selection  leads  to  the  mating  of  select  types,  so  that  those 
below  a  certain  standard  are  prevented  from  propagating,  it  follows 
that,  with  the  cessation  of  selection,  a  general  crossing  of  all  lyi)es, 
including  the  inferior  ones,  must  take  place,  and  thus  lower  the  average 
quality  of  the  whole  stock.  Weismann  explained  in  this  manner,  for 
instance,  the  prevalence  of  short-sightedness  among  civilized  people. 
The  individuals  with  defective  eyesight  not  being  weeded  out  in 
modern  society,  the  sharpness  of  the  eyesight  of  the  population  sinks 
gradually.     The  same  would  apply  to  the  deterioration  of  the  teeth 

263 


264     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

of  man,  of  the  breast-gland  of  modern  women,  etc.  The  fact  that 
degeneration  generally  progresses  so  slowly,  often  taking  thousands 
and  thousands  of  years,  seemed  to  him  a  sufficient  proof  of  the  inade- 
quacy of  the  Lamarck  ian  explanation.  For  if  the  effect  of  disuse  were 
transmitted  in  accumulating  ratio  in  the  successive  generations,  a 
useless  organ  ought  to  disappear  much  more  quickly. 

"Weismann  originally  attributed  a  great  effect  to  panmixia,  and 
considered  that  nearly  90  per  cent,  of  the  reduction  of  rudimentary 
organs  was  due  to  it;  the  remainder,  up  to  the  complete  loss  of  the 
organs,  being  accounted  for  by  reversed  selection.  Romanes  was 
much  more  modest  in  his  estimate,  and  only  allowed  about  10  to  20 
per  cent,  to  this  cause;  while  Lloyd  Morgan  gave  only  5  per  cent, 
reduction  of  the  original  size.  The  final  reduction  of  the  organ  to 
zero  is  still  not  accounted  for  by  any  of  these  theories.  Calling  to  aid 
a  failure  of  the  force  of  heredity,  as  Romanes  did,  can  hardly  be  con- 
sidered a  solution  of  the  problem.  First  of  all,  the  force  of  heredity 
does  not  explain  anything  in  the  case.  It  only  restates  the  problem. 
We  want  to  know  what  the  force  of  heredity  is.  Secondly,  if  the  force 
of  heredity  does  fail,  we  should  have  to  explain  why  it  wanes  in  some 
cases  and  not  in  others.  For  the  reduction  and  elimination  of  rudimen- 
tary organs  occurs  apparently  in  the  most  irregular,  haphazard  manner. 

''But  can  panmixia  really  reduce  an  organ ?  Plate,  in  agreement 
with  Spencer,  Eimer,  and  others,  denies  any  such  possibility.  An 
organ  in  a  given  condition  of  its  existence  varies  around  a  mean  or 
average,  the  plus  and  minus  variations  generally  being  equally  fre- 
quent. It  follows,  therefore,  that  if  all  the  existing  variations  are 
crossed  in  propagation,  the  organ  remains  stationary.  Selection  only 
improves  the  organ  by  cutting  off  the  minus  variations;  the  absence 
of  selection  would  simply  leave  the  organ  where  it  was  before  the 
selection.  At  most  it  could  only  sink  a  very  Httle  below  the  aver- 
age. That  this  is  so  is  seen  in  organs  which  are  not  under  the  sway  of 
selection  at  all.  There  are  numberless  such  indifferent  species  charac- 
ters, which  ought  gradually  to  dwindle  and  disappear,  yet  they  remain 
fairly  constant,  though  continually  exposed  to  the  swamping  effect 
of  panmixia.  Panmixia  may  explain  the  functional  degeneration  of 
an  organ,  but  cannot  explain  its  actual  rudimentation. 

"Weismann  himself  in  later  times  abandoned  panmixia  as  a  suffi- 
cient means  of  explanation,  and  resorted  to  a  new  theory — that  of 
germinal  selection."^ 

^  From  S.  Herbert,  First  Principles  of  Evolution  (19 13). 


OTHER  THEORIES  OF  SPECIES-FOR^UXG  265 

weismann's  theory  of  germinal  selection 
This  theory  was  intended  to  rehaljihtate  the  selection  principle 
which  had  lost  a  great  deal  of  prestige  because  of  the  serious  character 
of  the  objections  that  had  been  raised  against  it,  most  of  which  have 
been  stated  in  the  last  chapter.  The  theory  is  believed  by  its  author 
to  overcome  all  objections  and  doubts  and  to  clear  away  all  difficulties. 
"Its  strength,"  says  Plate,  "shall  avail  in  four  directions.  First,  it 
shall  explain  how  not  only  degeneration  (physiological)  but  rudimenta- 
tion  (morphological)  occurs  in  panmixia;  second,  why  exactly  those 
variations  needed  for  the  development  of  a  certain  adaptation  appear 
at  the  right  time;  third,  how  correlation  of  adaptation  comes  to  exist; 
and  fourth,  how  variations  are  able  to  develop  orthogenetically  along 
a  definite  line  without  depending  on  the  necessity  of  a  personal  selec- 
tion raising  them  step  by  step." 

The  essential  feature  of  germinal  selection,  as  the  name  implies, 
is  a  transfer  of  the  struggle  for  existence  to  the  germ  cell.  The  germ 
cell  is  assumed  to  be  a  greatly  reduced  and  simplified  sample  of  the 
characters  of  the  whole  organism.  Each  independently  variable  part 
of  the  organism  is  supposed  to  be  represented  in  the  germ  cell  by  a 
minute  physiological  unit,  unique  in  composition  and  capable  of 
reproducing  the  part  in  question  in  a  new  organism.  These  hereditary 
units  are  called  "determinants."  Thus  there  is  a  different  kind  of 
determinant  for  each  muscle  of  the  body,  for  each  bone,  or  for  each 
independently  functioning  blood  vessel;  but,  since  all  red  blood  cor- 
puscles are  alike,  there  would  be  only  one  determinant  for  all  of  them. 
These  determinants  have  to  grow,  and  in  cell  division,  to  divide  so  as  to 
furnish  to  daughter  germ  cells  all  of  the  necessary  determinants  for  a 
whole  individual.  In  their  process  of  growth  and  multiplication, 
which  goes  on  very  rapidly  at  certain  periods  in  the  germ-cell  cycle, 
these  determinants  are  in  competition  among  themselves  for  the 
available  food  supply.  Some  may  be  more  favorably  placed  than 
others  or  may  be  more  active  chemically  than  others.  There  will  thus 
arise  a  struggle  within  the  germ  for  a  chance  to  grow  and  reproduce 
their  kind,  which,  for  these  determinants,  might  be  as  bitter  as  would 
be  the  struggle  in  nature  among  the  whole  organisms  that  arc  in  com- 
petition for  a  place  in  the  world.  A  determinant  favored,  perhaps 
accidentally  or  possibly  because  of  inherent  activity,  by  a  good  food 
supply  would  wax  stronger  and  grow  faster  and  would,  logically,  pro- 
duce a  larger  and  more  effective  part  when  that  particular  germ  cell 
developed  into  an  adult.     Other  germ  cells  that  would  be  the  offspring 


266     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

of  this  germ  cell  would  continue  the  struggle  among  determinants,  and 
it  would  be  expected  that  the  strong  determinant  would  continue  to 
gain  further  advantage  until  the  structure  it  represents  reached  its 
maximum  efficiency.  Similarly,  a  determinant  that  was  for  some 
reason  deprived  of  its  fair  share  of  nutriment  at  any  time  would  be 
weakened  and  would  produce  in  cell  division  weakened  daughter 
determinants.  These  in  turn,  unless  especially  favored,  would  wage 
a  losing  fight  and  continue  to  grow  smaller  and  weaker.  Each  indi- 
vidual that  might  develop  from  such  germ  cells  would  have  the  charac- 
ters whose  determinant  had  been  weakened  in  a  reduced  and 
progressively  degenerating  condition.  Finally,  certain  determinants 
might  starve  entirely,  and  the  part  for  which  they  stood  would  dis- 
appear entirely  from  the  ontogeny  of  the  individual  arising  from  these 
germ  cells. 

In  this  way  Weismann  tried  to  explain  the  gradual  dwindling 
and  the  final  elimination  of  useless  organs.  So  also  he  would  explain 
definitely  directed  or  orthogenetic  variations,  because  germinal  selec- 
tion, once  started  in  a  given  direction,  continues  automatically  till 
the  goal  of  adaptiveness  is  reached. 

The  most  potent  objections  to  the  theory  of  germinal  selection  are 
as  follows: 

1.  There  should  be,  according  to  this  theory,  certain  pronounced 
tendencies  in  variability  in  definite  directions,  whereas  fluctuating 
variations  nearly  always  distribute  themselves  evenly  about  the  mean 
or  mode,  and  the  same  specific  mean  or  mode  is  stationary  in  succes- 
sive generations. 

2.  The  theory  implies  too  rapid  and  too  general  modification  of 
parts  and  therefore  does  not  accord  with  the  fact  that  species  are 
decidedly  constant,  except  for  occasional  mutations,  over  long  periods 
of  time.  To  meet  this  objection  Weismann  proposes  a  new  self- 
correcting  mechanism  that  checks  too  rapid  a  development  of  char- 
acters. 

3.  The  over-  or  undernourishment  of  determinants  might  con- 
ceivably induce  size  changes  in  characters  already  present,  but  could 
hardly  be  responsible  for  the  origin  of  qualitatively  different  characters. 

4.  Actual  experiments  in  over-  and  underfeeding  of  animals  have 
been  carried  on  by  certain  experimenters  in  order  to  test  out  the  theory 
of  germinal  selection.  In  the  experiments  of  Kellogg,  for  example, 
involving  feeding  silkworm  larvae  only  one-eighth  of  the  normal 
amount  of  food,  the  only  result  was  that  the  mature  individuals  were 


OTHER  THEORIES  OF  SPECIES-FOR.\HXG  267 

dwarfed  in  size.  The  relative  sizes  of  the  parts  were  unaltered,  show- 
ing that  there  had  been  no  real  struggle  among  the  determinants;  for, 
on  the  theory  of  germinal  selection,  only  the  stronger  determinants 
would  have  survived  and  the  weaker  ones  would  have  been  starved 
out.  Partial  individuals,  moreover,  lacking  certain  organs  and  over- 
developed in  others,  would  have  been  produced  instead  of  individuals 
merely  smaller  in  all  parts. 

These  are  the  specific  objections  to  the  theory,  but  more  important 
than  all  of  these  is  the  general  objection  that  follows: 

"Thus  Weismann,"  says  Morgan,^  ''has  piled  up  one  hypothesis 
on  another  as  though  he  could  save  the  integrity  of  the  theory  of 
natural  selection  by  adding  new  speculative  matter  to  it.  The  most 
unfortunate  feature  is  that  the  new  speculation  is  skilfully  removed 
from  the  field  of  verification,  and  invisible  germs  whose  sole  functions 
are  those  which  Weismann's  imagination  bestows  on  them,  are  brought 
forward  as  though  they  could  supply  the  deficiencies  of  Darwin's 
theory.  This  is,  indeed,  the  old  method  of  the  philosophizers  of 
nature.  An  imaginary  system  has  been  invented  which  attempts  to 
explain  all  difificulties,  and  if  it  fails,  then  new  inventions  are  to  be 
thought  of.  Thus  we  see  where  the  theory  of  selection  of  fluctuating 
germs  has  led  one  of  the  most  widely  known  disciples  of  the  Darwin- 
ian theory. 

''The  worst  feature  of  the  situation  is  not  so  much  that  Weismann 
has  advanced  new  hypotheses  unsupported  by  experimental  evidence, 
but  that  the  speculation  is  of  such  a  kind  that  it  is,  from  its  very 
nature,  unverifiable,  and  therefore  useless.  Weismann  is  mistaken 
when  he  assumes  that  many  zoologists  object  to  his  methods  because 
they  are  largely  speculative.  The  real  reason  is  that  the  speculation  is 
so  often  of  a  kind  that  cannot  be  tested  by  observation  and  experiment. " 

It  seems  almost  impossible  that  the  same  Professor  Morgan,  who 
wrote  the  foregoing  paragraphs  in  1903,  should  now  be  the  leading 
exponent  of  a  theory  of  the  mechanics  of  hereditary  transmission 
which  depends  upon  hereditary  units  almost  identical  with  Weis- 
mann's "determinants,"  for  the  "genes"  or  "factors"  of  Morgan  are 
minute  corporeal  bodies  in  the  germ  cells  which  determine  the  charac- 
ters of  the  adult  individual. 

The  difference  is,  however,  that  the  "genes"  of  Morgan  are  experi- 
mentally demonstrable  and  have  behind  them  a  vast  amount  of  real 
evidence  for  their  existence. 

^  From  T.  H.  Morgan,  Evolution  arid  Adaptation, 


268     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

In  this  chapter  the  writer  has  purposely  avoided  entering  into  the 
more  elaborate  intricacies  of  the  Weismannian  theories  of  develop- 
ment and  heredity.  The  theories  have  been  so  generally  discredited 
and  play  so  small  a  part  in  modern  biological  thought  that  it  seems 
useless  to  burden  the  reader's  mind  with  needless  complexities. 

Certain  other  phases  of  Weismann's  work,  especially  his  ideas  of 
the  germ  plasm,  its  separateness  and  its  continuity,  are  more  appro- 
priately studied  in  connection  with  genetics  than  at  the  present  time. 

ROUX'S  THEORY  OF  IXTRASELECTIOX  OR  THE  BATTLE  OF  THE  PARTS 

In  point  of  time  this  theory  antedates  Weismann's  theories,  since 
it  was  proposed  in  1881.  In  some  respects  it  is  a  more  acceptable 
theory  than  germinal  selection,  but  in  others  quite  unacceptable. 
The  theory  is  designed  primarily  to  explain  the  origin  of  the  "fine  and 
deHcate  inner  adaptations"  of  organisms,  which  do  not  come  in  con- 
tact with  the  external  environment  and  therefore  could  not  be  directly 
affected  by  it.  The  idea  is  that  there  is  a  sort  of  struggle  among  the 
tissues  for  a  chance  to  develop  in  the  direction  of  functional  perfection. 
Certain  contacts,  stresses,  and  pressures  of  part  on  part  aid  or  hinder 
the  development  of  parts.  Thus,  where  muscular  pressure  on  bone 
is  greatest  or  weight  borne  by  bone  is  greatest  there  will  the  most  bony 
tissue  be  laid  down  in  the  form  of  lamellae.  The  result  is  that  any 
given  bone  improves  its  structure  by  resistance  to  strain  and  pressure, 
which  is  a  case  of  improvement  with  use.  We  may  then  inquire  how 
such  a  change  in  the  individual  could  affect  the  evolution  of  the  race. 
The  only  reply  involves  the  adoption  of  a  distinctly  Lamarckian  con- 
cept, and  this  at  present  is  quite  unacceptable. 

COINCIDENT   SELECTION    OR    ORG.ANIC    SELECTION 

This  theory  has  been  masked  under  various  guises.  In  addition 
to  the  two  titles  given  above,  it  has  appeared  under  the  names  "onto- 
genetic selection"  and  "orthoplasy."  The  main  idea,  according  to 
Herbert,  is  that  "the  individually  acquired  characters,  though  not 
transmitted  to  the  offspring,  serve  to  tide  the  successive  generations 
over  the  critical  period  until  germinal  (inborn)  variations  of  the 
same  kind  appear  which  are  inheritable.  Ontogenetic  (individually 
acquired)  adaptations  and  natural  selection  work  together  towards  the 
same  end. 

"This  hypothesis  would  help  to  account  for  two  related  difficult 
points  in  the  theory  of  natural  selection.  Firstly,  it  would  explain 
the  possibihty  of  the  slow  accumulation  of  germinal  variations  in  their 


OTHEk  THEORIES  OF  SPECTES-FORMIXG  269 

first  stages  before  they  attain  selective  value;  seconclly,  it  would  make 
correlated  adaptations  feasible  by  supplying  ontogenetic  (individually 
acquired)  modifications,  until  the  material  for  the  api)ropriate  germi- 
nal adaptations  arose. 

"It  has  been  objected  to  this  theory  that,  since  the  individually 
acquired  modifications  possess  the  main  selective  value  in  these 
instances,  there  is  no  reason  why  the  corresponding  germinal  variations 
should  be  fostered  at  all.  The  individuals  with  the  right,  but  slight, 
congenital  variations  would  have  no  advantage  over  their  fellows  who 
show  no  such  coincident  variations.  Nor  is  there  any  ground  to 
assume  that  individuals  with  the  greatest  amount  of  plastic  modifica- 
tion in  a  given  direction  will  tend  to  exhibit  similar  innate  variations 
to  a  greater  degree  than  those  individuals  not  possessing  this  plas- 
ticity."^ 

ISOLATION   THEORIES 

One  of  the  objections  to  natural  selection  was  that  a  favorable 
variation  appearing  in  one  or  a  few  individuals  would  be  lost  because 
the  individuals  possessing  it  would  interbreed  with  those  not  possessing 
it,  which  presumably  would  be  much  more  numerous.  If  there  were 
any  kind  of  agency  whose  effect  would  be  a  partial  or  complete  inhibi- 
tion of  intercrossing,  the  favorable  character  would  have  a  chance  to 
survive. 

Several  related  theories  have  arisen  that  deal  with  possible  isola- 
tive  or  segregative  agencies  that  might  serve  to  prevent  promiscuous 
intercrossing,  and  these  have  received  the  names  geographic  isolation, 
climatic  isolation,  reproductive  isolation,  and  physiologic  isolation. 

Geographic  isolation. — Moritz  Wagner  was  the  founder  of  this 
theory.  He  was  a  very  extensive  traveler  and  had  a  vast  knowledge 
of  the  details  of  the  geographic  distribution  of  animals.  He  believed 
that  isolation  was  absolutely  essential  in  the  differentiation  of  species. 
He  at  first  thought  of  his  theory  as  auxiliary  to  natural  selection,  but 
later,  strongly  impressed  by  the  facts  he  had  collected,  he  concluded 
that  isolation  was  an  independent  and  alternative  explanation  of 
species-forming.  The  underlying  idea  is  one  that  has  already  received 
attention  in  chapter  vii,  under  ''Evidences  from  Geographic  Distri- 
bution." Any  successful  species  tends  to  spread  in  all  directions  until 
checked  by  barriers.  Some  few  members  of  a  species  under  favorable 
conditions  may  surmount  the  barrier  and  become  isolated.     The  result 

^  From  S.  Herbert,  First  Principles  oj  Evolution  (19 13). 


270     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

will  be  that,  if  they  differ  in  any  definite  way  from  the  main  body  of 
the  species,  a  new  elementary  species  will  at  once  gain  a  foothold  and 
will  evolve  independently  of  the  parent-species.  If  a  certain  area  of 
land  is  cut  off  from  a  continent  so  as  to  form  a  continental  island-,  the 
members  of  each  species  that  have  become  isolated  will  evolve  independ- 
ently of  the  main  body  of  the  species  and  will  have  their  own  peculiar 
lines  of  variation  preserved  from  back-crossing  with  the  parent-species. 

Professor  David  Starr  Jordan,^  the  leading  proponent  of  the  theory 
of  geographic  isolation  in  America  says : 

"It  is  now  nearly  forty  years  since  Moritz  Wagner  (1868)  first 
made  it  clear  that  geographic  isolation  {rdumlicke  Sojuierung)  was  a 
factor  or  condition  in  the  formation  of  every  species,  race,  or  tribe  of 
animal  or  plant  we  know  on  the  face  of  the  earth.  This  conclusion 
is  accepted  as  almost  self-evident  by  every  competent  student  of 
species  or  of  the  geographical  distribution  of  species.  But  to  those 
who  approach  the  subject  of  evolution  from  some  other  side  the 
principles  set  forth  by  Wagner  seem  less  clear.  They  have  never  been 
confuted,  scarcely  ever  attacked,  so  far  as  the  present  writer  remem- 
bers, but  in  the  literature  of  evolution  of  the  present  day  they  have 
been  almost  universally  ignored.  Nowadays  much  of  our  discussion 
turns  on  the  question  of  whether  or  not  minute  favorable  variations 
would  enable  their  possessors  little  by  little  to  gain  on  the  parent  stock, 
so  that  a  new  race  would  be  established  side  by  side  with  the  old,  or  on 
whether  a  wide  fluctuation  or  mutation  would  give  rise  to  a  new  species 
which  would  hold  its  own  in  competition  with  the  parent.  In  theory, 
either  of  these  conditions  might  exist.  In  fact,  both  of  them  are 
virtually  unknown.  In  nature  a  closely  related  distinct  species  is  not 
often  quite  side  by  side  with  the  old.  It  is  simply  next  to  it,  geo- 
graphically or  geologically  speaking,  and  the  degree  of  distinction 
almost  always  bears  a  relation  to  the  importance  or  the  permanence 
of  the  barrier  separating  the  supposed  new  stock  from  the  parent 
stock. 

"A  flood  of  light  may  be  thrown  on  the  theoretical  problem  of  the 
origin  of  species  by  the  study  of  the  probable,  actual  origin  of  species 
with  which  we  are  familiar  or  of  which  the  actual  history  or  the  actual 
ramifications  may  in  some  degree  be  traced. 

*'In  regions  broken  by  few  barriers,  migration  and  interbreeding 
being  allowed,  we  find  widely  distributed  species,  homogeneous  in  their 
character,  the  members  showing  individual  fluctuation  and  climatic 

^  Science,  N.S.,  Vol.  XXII  (1905). 


OTHER  THEORIES  OF  SPECIES-FORMING  27 1 

effects,  but  remaining  uniform  in  most  regards,  all  representatives 
slowly  changing  together  in  the  process  of  adaptation  by  natural 
selection.  In  regions  broken  by  barriers  which  isolate  groups  of  indi- 
viduals we  find  a  great  number  of  related  species,  though  in  most  cases 
the  same  region  contains  a  smaller  number  of  genera  or  families.  In 
other  words,  the  new  species  will  be  formed  conditioned  on  isolation, 
though  these  same  barriers  may  shut  out  altogether  forms  of  life  which 
would  invade  the  open  district. 

''  Given  any  species  in  any  region,  the  nearest  related  species  is  not 
likely  to  be  found  in  the  same  region  nor  in  a  remote  region,  but  in  a 
neighboring  district  separated  from  the  first  by  a  barrier  of  some  sort. 

''Doubtless  wide  fluctuations  or  mutations  in  every  species  are 
more  common  than  we  suppose.  With  free  access  to  the  mass  of 
the  species,  these  are  lost  through  interbreeding.  Isolate  them  as  in 
a  garden  or  an  enclosure  or  on  an  island,  and  these  may  be  con- 
tinued and  intensified  to  form  new  species  or  races.  Any  horticul- 
turist will  illustrate  this. 

''In  all  these  and  in  similar  cases  we  may  confidently  affirm:  The 
adaptive  characters  a  species  may  present  are  due  to  natural  selection 
or  are  developed  in  connection  with  the  demands  of  competition. 
The  characters,  non-adaptive,  which  chiefly  distinguish  species  do  not 
result  from  natural  selection,  but  from  some  form  of  geographical 
isolation  and  the  segregation  of  individuals  resulting  from  it." 

J.  T.  Gulick,  another  exponent  of  the  efficacy  of  geographic  isola- 
tion in  species-forming,  has  offered  in  evidence  of  his  views  facts  about 
the  distribution  of  Hawaiian  land  snails.  In  the  island  of  Oahu,  for 
example,  the  volcanic  ridges  have  been  eroded  out  into  a  series  of 
isolated  valleys  in  the  bottoms  of  which  grows  abundant  vegetation, 
while  on  the  highlands  there  is  little  but  barren  rock.  The  climatic 
conditions  of  all  the  numerous  valleys  are  the  same,  but,  remarkably 
enough,  each  variety  of  snail  is  confined  not  only  to  one  island,  but  to 
a  definite  valley  on  an  island.  The  degree  of  difference,  moreover, 
between  varieties  is  in  proportion  to  the  distance  that  separates  them. 
Gulick  claimed  that  he  was  able  to  estimate  the  degree  of  divergence 
between  the  snails  of  any  two  valleys  by  measuring  the  number  of 
miles  that  lay  between  them.  Gulick's  findings  have  been  extensively 
corroborated  by  recent  explorations  on  the  snails  of  other  oceanic 
islands  by  Crampton. 

An  interesting  type  of  isolation  that  hardly  can  be  termed  geo- 
graphic, yet  is  essentially  equivalent  to  the  latter  in  its  efl"ects,  is  found 


272     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

in  connection  with  the  extensive  group  of  Hce  (Mallophaga)  that  Hve 
their  whole  hves  buried  among  the  feathers  of  birds  or  the  hair  of 
mammals.  These  animals  cannot  fly  and  are  quite  effectively  isolated 
for  life  upon  a  particular  bird.  They  do,  however,  during  the  intimate 
period  of  nesting,  pass  from  parent  to  offspring,  so  that  they  may  be 
said  to  be  isolated  upon  definite  genetic  lines.  In  the  case,  especially, 
of  birds  like  the  eagle,  a  bird  of  long  life  and  monogamous  habits,  the 
parasite  becomes  as  isolated  as  might  be  a  race  on  a  small  island.  The 
result  is  that  sometimes  the  lice  of  a  single  bird  and  its  offspring  are 
of  quite  a  distinct  variety,  which  has  become  fixed  by  inbreeding  until 
a  high  degree  of  uniformity  has  been  attained.  Such  an  isolated 
variety  may  be  almost  as  distinct  as  a  true  species.  Obviously  in  this 
case,  as  in  others,  isolation  must  have  had  a  real  effect  upon  species- 
forming  quite  apart  from  natural  selection,  except  in  so  far  as  the  unfit 
variants  have  not  survived. 

The  writer's  impression  is  that  isolation  as  a  factor  in  evolution 
has  been  undervalued  by  the  majority  of  writers  on  the  subject.  It  is 
a  highly  important  and  essential  factor  in  the  establishment  of  species. 
If  natural  selection  may  be  said  to  be  the  prime  factor  in  producing 
adaptations,  isolation  may  be  said  to  be  the  prime  factor  in  species 
differentiation,  guided  only  within  moderate  limits  by  natural  selection. 

Biologic  isolation. — The  effects  of  this  type  of  isolation  are  not 
nearly  so  well  established  as  are  those  of  geographic  isolation.  Accord- 
ing to  this  theory,  differences  in  the  rate  of  development  or  earliness 
or  lateness  of  the  breeding  season  would  serve  to  prevent  certain 
varieties  from  intercrossing.  Only  those  individuals  which  were 
sexually  active  simultaneously  would  mate,  and  individuals  with 
different  breeding  times  and  seasons  would  be  isolated  from  one 
another  and  would  likely  maintain  the  variations  that  arose  in  the 
isolated  stocks.  The  main  weakness  of  this  phase  of  isolation  is, 
however,  that  we  have  so  little  actual  evidence  that  it  is  operative  in 
nature. 

Reproductive  isolation. — A  much  more  real  type  of  isolation  than 
the  last  named  is  involved  in  reproduction.  Several  conditions  may 
arise  of  entirely  distinct  sorts  that  will  tend  to  inhibit  mating  at  ran- 
dom. The  first  agency  has  been  called  "assortative  mating"  and 
impUes  a  sort  of  race  feeling  involving  either  a  special  attraction  of  like 
for  like,  based  on  similarity  of  odors,  colors,  etc.,  or  an  antipathy 
toward  opposites  or  unlikes.  The  inhibition  to  general  mating  may 
Involve  a  mere  mechanical  lack  of  fit  in  certain  organs  necessary  for 


OTHER  THEORIES  OF  SPECIES-FORMING  273 

successful  mating.  Such  conditions  are  readily  observable  between 
closely  allied  species.  Again,  the  prevention  of  intercrossing  may 
result  from  the  appearance  of  a  lowered  interfertility  between  the 
variant  individuals  and  those  of  the  parent-stock.  If  individuals 
varying  in  the  same  direction  were  even  slightly  more  fertile  inter  se 
than  those  varying  in  different  directions  there  would  be  a  progressive 
tendency  in  a  series  of  generations  for  the  varying  individuals  to 
diverge  more  and  more  markedly,  and  ultimately  to  become  practi- 
cally sterile  except  with  members  of  their  own  group. 

That  environmental  changes  do  frequently  affect  the  fertility  of 
animals  is  seen  when  wild  animals  are  kept  in  confinement.  Rela- 
tively few  wild  animals  breed  in  captivity.  Such  a  lowering  of  fer- 
tility as  the  result  of  environmental  changes  might  restrict  crossing 
between  unlike  forms,  while  permitting  it  among  the  like  ones. 

Summary  on  isolation  theories. — There  is  a  great  divergence  of 
opinion  as  to  the  importance  of  isolation  as  a  causal  factor  in  species- 
forming.  Some  writers,  such  as  D.  S.  Jordan  and  V.  L.  Kellogg,  con- 
sider isolation  an  indispensable,  and  therefore  primary,  factor;  others, 
especially  geneticists,  almost  ignore  it  as  an  effective  factor.  Still 
others,  like  the  present  writer,  take  a  middle  ground  and  conclude 
that  isolation,  especially  geographic  isolation,  has  helped  greatly  in  the 
segregation  and  establishment  of  well-defined  groups  such  as  species 
or  varieties,  the  latter  developing  into  the  former  after  prolonged 
isolation  and  the  addition  of  new  variations.  Isolation  theories,  how- 
ever, have  no  light  to  shed  upon  the  difficult  problem  of  adaptation, 
and  it  is  here  that  isolation  is  auxiliary  to  natural  selection. 

THEORIES   ALTERNATIVE   TO   NATURAL   SELECTION 

The  three  theories  that  have  been  offered  by  their  authors  as  sub- 
stitutes for  natural  selection  are: 

1.  Theory  of  the  inheritance  of  acquired  characters  commonly  called 
Lamarckism:  This  theory  has  been  outlined  in  the  chapter  on  the 
history  of  evolution  (pp.  19  ff.).  It  will  again  be  dealt  with  in  con- 
siderable detail  in  chapter  xxii.  For  the  present,  then,  we  may  pass 
by  this  theory  without  further  comment. 

2.  The  orthogenesis  theories:  These  theories  have  already  been 
presented  in  sufficient  detail  for  our  purposes  in  chapter  ii  (pp.  t,^  ff.). 

3.  The  mutation  theory  of  Hugo  De  Vries:  This  theory  has  been 
dealt  with  in  chapter  ii,  and  will  be  discussed  in  further  detail  in 
chapter  xxiv. 


274      READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

4.  The  tetrakinetic  theory  of  H.  F.  Oshorn:  This  is  a  recent  restate- 
ment in  energistic  terms,  of  the  causo-mechanical  basis  of  evolution. 
It  is  placed  in  the  next  chapter,  but  cannot  fully  be  understood  until 
the  subject  of  genetics  has  been  presented. 

It  is  almost  impossible  satisfactorily  to  pursue  a  further  study  of 
the  causal  factors  of  evolution  without  encroaching  upon  the  field  that 
is  now  called  genetics,  and  so  we  shall  pass  without  further  explana- 
tions to  a  consideration  of  this  field  of  experimental  and  analytical 
evolution. 


CHAPTER  XIX 

A   NEW   COMPOSITE    CAUSO-MECHANICAL    THEORY   OF 
EVOLUTION  (THE  TETR AKINETIC  THEORY)^ 

HENRY   FAIRFIELD    OSBORN 
THE   ENERGY   CONCEPT   OF   LIFE 

While  we  owe  to  matter  and  form  the  revelation  of  the  existence 
of  the  great  law  of  evolution,  we  must  reverse  our  thought  in  search 
for  causes  and  take  steps  toward  an  energy  conception  of  the  origin 
of  life  and  an  energy  conception  of  the  nature  of  heredity. 

So  far  as  the  creative  power  of  energy  is  concerned,  we  are  on  sure 
ground:  in  physics  energy  controls  matter  and  form;  in  physiology 
function  controls  the  organ;  in  animal  mechanics  motion  controls 
and,  in  a  sense,  creates  the  form  of  muscles  and  bones.  In  every 
instance  some  kind  of  energy  or  work  precedes  some  kind  of  form, 
rendering  it  probable  that  energy  also  precedes  and  controls  the 
evolution  of  life. 

The  total  disparity  between  invisible  energy  and  visible  form  is 
the  second  point  which  strikes  us  as  in  favor  of  such  a  conception, 
because  the  most  phenomenal  thing  about  the  heredity-germ  is  its 
microscopic  size  as  contrasted  with  the  titanic  beings  which  may  rise 
out  of  it.  The  electric  energy  transmitted  through  a  small  copper 
wire  is  yet  capable  of  moving  a  long  and  heavy  train  of  cars.  The 
discovery  by  Becquerel  and  Curie  of  radiant  energy  and  of  the  proper- 
ties of  radium  the  energy  per  unit  of  mass  is  enormously  greater  than 
the  energy  quanta  which  we  were  accustomed  to  associate  with  units 
of  mass;  whereas,  in  most  man-made  machines  with  metallic  wheels 
and  levers,  and  in  certain  parts  of  the  animal  machine  constructed  of 
muscle  and  bone,  the  work  done  is  proportionate  to  the  size  and  form. 
The  slow  dissipation  or  degradation  of  energy  in  radium  has  been 
shown  by  Curie  to  be  concomitant  with  the  giving  off  of  an  enormous 
amount  of  heat,  while  Rutherford  and  Strutt  declare  that  in  a  very 
minute  amount  of  active  radium  the  energy  of  degradation  would 
entirely  dominate  and  mask  all  other  cosmic  modes  of  transformation 

^  From  H.  F.  Osborn,  TJie  Origin  and  Evolution  of  Life  (copyright  19 16).  Used 
by  special  permission  of  the  publishers,  Charles  Scribner's  Sons. 

275 


276     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

of  energy;  for  example,  it  far  outweighs  that  arising  from  the  gravita- 
tional energy  which  is  an  ample  supply  for  our  cosmic  system,  the 
explanation  being  that  the  minutest  energy  elements  of  which  radium 
is  composed  are  moving  at  incredible  velocities,  approaching  often 
the  velocity  of  light,  i.e.,  180,000  miles  per  second.  The  energy  of 
radium  differs  from  the  supposed  energy  of  life  in  being  constantly 
dissipated  and  degraded;  its  apparently  unlimited  power  is  being 
lost  and  scattered. 

We  may  imagine  that  the  energy  which  lies  in  the  life-germ  of 
heredity  is  very  great  per  unit  of  mass  of  the  matter  which  contains 
it,  but  that  the  life-germ  energy,  unlike  that  of  radium,  is  in  process 
of  accumulation,  construction,  conservation,  rather  than  of  dissipation 
and  destruction. 

Following  the  time  (1620)  when  Francis  Bacon  divined  that  heat 
consists  of  a  kind  of  motion  or  brisk  agitation  of  the  particles  of 
matter,  it  has  step  by  step  been  demonstrated  that  the  energy  of  heat, 
of  light,  of  electricity,  the  electric  energy  of  chemical  configurations, 
the  energy  of  gravitation,  are  all  utilized  in  living  as  well  as  in  lifeless 
substances.  Moreover,  no  form  of  energy  has  thus  far  been  discovered 
in  living  substances  which  is  peculiar  to  them  and  not  derived  from 
the  inorganic  world.  In  a  broad  sense  all  these  manifestations  of 
energy  are  subject  to  Newton's  dynamical  laws  which  were  formulated 
in  connection  with  the  motions  of  the  heavenly  bodies,  but  are  found 
to  apply  equally  to  all  motions  great  or  little. 

These  three  fundamental  laws  are  as  follows : 

I  I 

Corpus  omne  perseverare  in  statu  suo  Every  body  perseveres  in  its  state  of 

quiescendi  v^el  movendi  uniformiter  in  rest,  or  of  uniform  motion  in  a  right 

directum,  nisi  quatenus  illud  a  viribus  line,  unless  it  is  compelled  to  change 

impressis  cogitur  statum  suum  mutare.  that  state  by  forces  impressed  thereon. 

II  II 

Mutationem  motus  proportionalem  The    alteration    of   motion   is    ever 

esse  vi  motrici  impressae,  et  fieri  secun-  proportional  to  the  motive  force  im- 
dum  lineam  rectam  qua  vis  ilia  im-  pressed;  and  is  made  in  the  direction  of 
primitur.  the  right  line  in  which  that  force  is 

impressed. 

III  III 

Actioni  contrariam  semper  et  aequa-  To    every    action    there    is    always 

lem  esse  reactionem:    sive  corporum  opposed    an    equal    reaction:     or    the 

duorum  actione?  in  se  mutuo  semper  mutual  actions  of  two  bodies  upon  each 

esse  aequales  et  in  partes  contrarias  other  are  always  equal,  and  directed  to 

dirigi.  contrary  parts. 


THE  TETRAKINETIC  THEORY  277 

Newton's  third  law  of  the  equaUty  of  action  and  reaction  is  the 
foundation  of  the  modern  doctrine  of  energy,  not  only  in  the  Newto- 
nian sense  but  in  the  most  general  sense.  Newton  divined  the  prin- 
ciple of  the  conservation  of  energy  in  mechanics;  Rumford  (1798) 
maintained  the  universality  of  the  laws  of  energy;  Joule  (1843) 
established  the  particular  principle  of  the  conservation  of  energy, 
namely  the  exact  equivalence  between  the  amount  of  heat  produced 
and  the  amount  of  mechanical  energy  destroyed;  and  Helmholtz,  in 
his  great  memoir  tjber  die  Erhaltung  der  Kraft,  extended  this  system 
of  conservation  of  energy  throughout  the  whole  range  of  natural 
phenomena.  A  familiar  instance  of  the  so-called  transformation  of 
energy  is  where  the  sudden  arrest  of  a  cool  but  rapidly  moving  body 
produces  heat.     This  was  developed  as  ih.Q  first  law  of  thermodynamics. 

At  the  same  time  there  arose  the  distinction  between  potential 
energy,  which  is  stored  away  in  some  latent  form  or  manner  so  that 
it  can  be  drawn  upon  for  work — such  energy  being  exemplified  me- 
chanically by  the  bent  spring,  chemically  by  gunpowder,  and  elec- 
trically by  a  Leyden  jar — and  kinetic  energy,  the  active  energy  of 
motion  and  of  heat. 

While  all  active  mechanical  energy  or  work  may  be  converted 
into  an  equivalent  amount  of  heat,  the  opposite  process  of  turning 
heat  into  work  involves  more  or  less  loss,  dissipation,  or  degradation 
of  energy.  This  is  known  as  the  second  law  of  thermodynamics  and  is 
the  outgrowth  of  a  principle  discovered  by  Sadi  Carnot  (1824)  and 
developed  by  Kelvin  (1852,  1853).  The  far-reaching  conception  of 
cyclic  processes  in  energy  enunciated  in  Kelvin's  principle  of  the 
dissipation  of  available  energy  puts  a  diminishing  limit  upon  the 
amount  of  heat  energy  available  for  mechanical  purposes.  The  avail- 
able kinetic  energy  of  motion  and  of  heat  which  we  can  turn  into  work 
or  mechanical  effect  is  possessed  by  any  system  of  two  or  more  bodies 
in  virtue  of  the  relative  rates  of  motion  of  their  parts,  velocity  being 
essentially  relative. 

These  two  great  dynamical  principles  that  the  energy  of  motion 
can  be  converted  into  an  equivalent  amount  of  heat,  and  that  a  certain 
amount  of  heat  can  be  converted  into  a  more  limited  amount  of  power 
were  discovered  through  observations  on  the  motions  of  larger  masses 
of  matter,  but  they  are  believed  to  apply  equally  to  such  motions  as 
are  involved  in  the  smallest  electrically  charged  atoms  (ions)  of  the 
chemical  elements  and  the  particles  flying  off  in  radiant  energy  as 
phosphorescence.     Such  movements  of  infinitesimal  particles  undcrhc 


278      READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

all  the  physicochemical  laws  of  action  and  reaction  which  have  been 
observed  to  occur  within  living  things.  In  all  physicochemical 
processes  within  and  without  the  organism  by  which  energy  is  cap- 
tured, stored,  transformed,  or  released  the  actions  and  reactions  are 
equal,  as  expressed  in  Newton's  third  law. 

Actions  and  reactions  refer  chiefly  to  what  is  going  on  between 
the  parts  of  the  organism  in  chemical  or  physical  contact,  and  are 
subject  to  the  two  dynamical  principles  referred  to  above.  Inter- 
actions, on  the  other  hand,  refer  to  what  is  going  on  between  material 
parts  which  are  connected  with  each  other  by  other  parts,  and  cannot 
be  analyzed  at  all  by  the  two  great  dynamical  principles  alone  without 
a  knowledge  of  the  structure  which  connects  the  interacting  parts. 
For  example,  in  interaction  between  distant  bodies  the  cause  may  be 
very  feeble,  yet  the  potential  or  stored  energy  which  may  be  liberated 
at  a  distant  point  may  be  tremendous.  Action  and  reaction  are 
chiefly  simultaneous,  whereas  interaction  connects  actions  and  reac- 
tions which  are  not  simultaneous;  to  use  a  simple  illustration:  when 
one  pulls  at  the  reins  the  horse  feels  it  a  little  later  than  the  moment 
at  which  the  reins  are  pulled — there  is  interaction  between  the  hand 
and  the  horse's  mouth,  the  reins  being  the  interacting  part.  An 
interacting  nerve-impulse  starting  from  a  microscopic  cell  in  the  brain 
may  give  rise  to  a  powerful  muscular  action  and  reaction  at  some 
distant  point.  An  interacting  enzyme,  hormone,  or  other  chemical 
messenger  circulating  in  the  blood  may  profoundly  modify  the  growth 
of  a  great  organism. 

Out  of  these  physicochemical  principles  has  arisen  the  conception 
of  a  living  organism  as  composed  of  an  incessant  series  of  actions  and 
reactions  operating  under  the  dynamical  laws  which  govern  the 
transfer  and  transformation  of  energy. 

The  central  theory  which  is  developed  in  our  speculation  on  the 
Origin  of  Life  is  that  every  physicochemical  action  and  reaction 
concerned  in  the  transformation,  conservation,  and  dissipation  of 
energy,  produces  also,  either  as  a  direct  result  or  as  a  hy-product  a 
physicochemical  agent  of  interaction  which  permeases  and  affects  the 
organism  as  a  whole  or  affects  only  some  special  part.  Through  such 
interaction  the  organism  is  made  a  unit  and  acts  as  one,  because  the 
activities  of  all  its  parts  are  correlated.  This  idea  may  be  expressed 
in  the  following  simplified  scheme  of  the  functions  or  physiology  of  the 
organism : 


THE  TETRAKINETIC  THEORY 


279 


Action 

AND 

Reaction 


.  Interaction  . 


Action 

AND 

Reaction 


Functions  of  the                           Functions  of  the  Functions  of  the 

Capture,   Storage,                    Coordination,  Balance,  Capture,   Storage, 

and  Release  of                   Cooperation,  Compensation,  and  Release  of 

Energy                           Acceleration,  Retardation,  Energy 

of  Actions  and  Reactions 

Since  it  is  known  that  7na}iy  actions  and  reactions  of  the  organ- 
ism— such  as  those  of  general  and  locaUzed  growth,  of  nutrition,  of 
respiration — are  coordinated  with  other  actions  and  reactions  through 
interaction,  it  is  but  a  step  to  extend  the  principle  and  suppose  that 
all  actions  and  reactions  are  similarly  coordinated;  and  that  while 
there  was  an  evolution  of  action  and  reaction  there  was  also  a  cor- 
responding evolution  of  interaction,  for  without  this  the  organism 
would  not  evolve  harmoniously. 

Evidence  for  such  universality  of  the  interaction  principle  has 
been  accumulating  rapidly  of  late,  especially  in  experimental  medicine 
and  in  experimental  biology.  It  is  a  further  step  in  our  theory  to 
suppose  that  the  directing  power  of  heredity  which  regulates  the  initial 
and  all  the  subsequent  steps  of  development  in  action  and  reaction, 
gives  the  orders,  hastens  development  at  one  point,  retards  it  at 
another,  is  an  elaboration  of  the  principle  of  interaction.  In  lowly 
organisms  like  the  monads  these  interactions  are  very  simple;  in 
higher  organisms  like  man  these  interactions  are  elaborated  through 
physicochemical  and  other  agents,  some  of  which  have  already  been 
discovered  although  doubtless  many  more  await  discovery.  Thus  we 
conceive  of  the  origin  and  development  of  the  organism  as  a  con- 
comitant evolution  of  the  action,  reaction,  and  interaction  of  energy. 
Actions  and  reactions  are  borrowed  from  the  inorganic  world,  and 
elaborated  through  the  production  of  the  new  organic  chemical 
compounds;  it  is  the  peculiar  evolution  and  elaboration  of  the  physi- 
cal principle  of  interaction  which  distinguishes  the  living  organism. 

Thus  the  evolution  of  life  may  be  rewritten  in  terms  of  invi  sibe 
energy,  as  it  has  long  since  been  written  in  terms  of  visible  form.  All 
visible  tissues,  organs,  and  structures  are  seen  to  be  the  more  or  less 
simple  or  elaborate  agents  of  the  different  modes  of  energy.  One 
after  another  special  groups  of  tissues  and  organs  are  created  and  co- 
ordinated— organs  for  the  capture  of  energy  from  the  morganic  environ- 
ment and  from  the  Hfe  environment,  organs  for  the  storage  of  energy, 
organs  for  the  transformation  of  energy  from  the  potential  state  into 


28o     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

the  states  of  motion  and  heat.  Other  agents  of  control  are  evolved  to 
bring  about  a  harmonious  balance  between  the  various  organs  and 
tissues  in  which  energy  is  released,  hastened  or  accelerated,  slowed  down 
or  retarded,  or  actually  arrested  or  inhibited. 

In  the  simplest  organisms  energy  may  be  captured  while  the 
organism  as  a  whole  is  in  a  state  of  rest;  but  at  an  early  stage  of  life 
special  organs  of  locomotion  are  evolved  by  which  energy  is  sought 
out,  and  organs  of  prehension  by  which  it  may  be  seized.  Along  with 
these  motor  organs  are  developed  organs  of  ofense  and  defense  of 
many  kinds,  by  means  of  which  stored  energy  is  protected  from  cap- 
ture or  invasion  by  other  organisms.  Finally,  there  is  the  most 
mysterious  and  comprehensive  process  of  all,  by  which  all  these 
manifold  modes  of  energy  are  reproduced  in  another  organism. 

THE  FOUR  COMPLEXES  OF  ENERGY 

The  theoretic  evolution  of  the  four  complexes  is  somewhat  as 
follows: 

1.  In  the  order  of  time  the  Inorganic  Environment  comes  first; 
energy  and  matter  are  first  seen  in  the  sun,  in  the  earth,  in  the  air, 
and  in  the  water — each  a  very  wonderful  complex  of  energies  in  itself. 
They  form,  nevertheless,  an  entirely  orderly  system,  held  together  by 
gravitation,  moving  under  Newton's  laws  of  motion,  subject  to  the 
more  newly  discovered  laws  of  thermodynamics.  In  this  complex  we 
observe  actions  and  reactions,  the  sum  of  the  taking  in  and  giving 
out  of  energy,  the  conservation  of  energy.  We  also  observe  inter- 
actions wherein  the  energy  released  at  certain  points  may  be  greater 
than  the  energy  received,  which  is  merely  a  stimulus  for  the  beginning 
of  the  local  energy  transformations.  This  energy  is  distributed  among 
the  eighty  or  more  chemical  elements  of  the  sun  and  other  stars. 
These  elements  are  combined  in  plants  into  complex  substances,  gener- 
ally with  a  storage  of  energy.  Such  substances  are  disintegrated  into 
simple  substances  in  animals,  generally  with  a  release  of  energy.  All 
these  processes  are  termed  by  us  physicochemical. 

2.  With  life  something  new  appears  in  the  universe,  namely,  a 
union  of  the  internal  and  external  adjustment  of  energy  which  we 
appropriately  call  an  Organism.  In  the  course  of  the  evolution  of  life 
every  law  and  property  in  the  physicochemical  world  is  turned  to 
advantage;  every  chemical  element  is  assembled  in  which  inorganic 
properties  may  serve  organic  functions.  There  is  an  immediate  or 
gradual  separation  of  the  organism  into  two  complexes  of  energy, 


THE  TETRAKINETIC  THEORY  281 

namely,  first,  the  energy  complex  of  the  organism,  which  is  perishable 
with  the  term  of  life  of  the  individual,  and  second,  the  germ  or  heredity 
substance,  which  is  perpetual. 

3.  The  idea  that  the  germ  is  an  energy  complex  is  an  as  yet  un- 
proved hypothesis;  it  has  not  been  demonstrated.  The  Heredity-Germ 
in  some  respects  bears  a  likeness  to  latent  or  potential  interacting 
energy,  while  in  other  respects  it  is  entirely  unique.  The  supposed 
germ  energy  is  not  only  cumulative  but  is  in  a  sense  imperishable,  self- 
perpetuating,  and  continuous  during  the  whole  period  of  the  evolution 
of  life  upon  the  earth,  a  conception  which  we  owe  chiefly  to  the  law  of 
the  continuity  of  the  germ-plasm  formulated  by  Weismann.  Some 
of  the  observed  phenomena  of  the  germ  in  Heredity  are  chiefly 
analogous  to  those  of  interaction  in  the  Organism,  namely,  directive 
of  a  series  of  actions  and  reactions,  but  in  general  we  know  no  complete 
physical  or  inorganic  analogy  to  the  phenomena  of  heredity;  they  are 
unique  in  nature. 

4.  With  the  multiplication  and  diversification  of  individual  or- 
ganisms there  enters  a  new  factor  in  the  environment,  namely,  the 
energy  complex  of  the  Life  Environment. 

Thus  there  are  combined  certainly  three  and,  possibly,  four  com- 
plexes of  energy,  of  which  each  has  its  own  actions,  reactions,  and 
interactions.  The  evolution  of  life  proceeds  by  sustaining  these 
actions,  reactions,  and  interactions  and  constantly  building  up  new 
ones :  at  the  same  time  the  potentiality  of  reproducing  these  actions,  re- 
actions, and  interactions  in  the  course  of  the  development  of  each  new 
organism  is  gradually  being  accumulated  and  perpetuated  in  the  germ. 

From  the  very  beginning  every  individual  organism  is  competing 
with  other  organisms  of  its  own  kind  and  of  other  kinds,  and  the  law 
of  the  survival  of  the"  fittest  is  operating  between  the  forms  and  func- 
tions of  organisms  as  a  whole  and  between  their  separate  actions, 
reactions,  and  interactions.  This,  as  Weismann  pointed  out,  while 
apparently  a  selection  of  the  individual  organism  itself,  is  actually  a 
selection  of  the  heredity-germ  complex,  of  its  potentialities,  powers, 
and  predispositions.  Thus  Selectioii  is  not  a  form  of  energy,  nor  a 
part  of  the  energy  complex;  it  is  an  arbiter  between  different  com- 
plexes and  forms  of  energy;  it  antedates  the  origin  of  life  just  as 
adaptation  or  fitness  antedates  the  origin  of  life,  as  remarked  by 
Henderson. 

Thus  we  arrive  at  a  conception  of  the  relations  of  organisms  to 
each  other  and  to  their  environment  as  of  an  enormous  and  always 


282     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

increasing  complexity,  sustained  through  the  interchange  of  energy. 
Darwin's  principle  of  the  survival  or  elimination  of  various  forms  of 
living  energy  is,  in  fact,  adumbrated  in  the  survival  or  elimination  of 
various  forms  of  lifeless  energy  as  witnessed  among  the  stars  and 
planets.  In  other  words,  Darwin's  principle  operates  as  one  of  the 
causes  of  evolution  in  making  the  lifeless  and  living  worlds  what  they 
now  appear  to  be,  but  not  as  one  of  the  energies  of  evolution.  Selec- 
tion merely  determines  which  one  of  a  combination  of  energies  shall 
survive  and  which  shall  perish. 

The  complex  of  four  interrelated  sets  of  physicochemical  energies 
which  I  have  previously  set  forth  as  the  most  fundamental  biologic 
scheme  or  principle  of  development  may  now  be  restated  as  follows: 

In  each  organism  the  phenomena  of  life  represent  the  action,  reaction, 
and  interaction  of  four  complexes  of  physicochemical  energy,  namely, 
those  of  (j)  the  Inorganic  Environment,  (2)  the  developing  Organism 
{protoplasm  and  hody-chromatin) ,  (3)  the  germ  or  Heredity -Chromatin, 
{4)  the  Life  Environment.  Upon  the  resultant  actions,  reactions^  and 
interactions  of  potential  and  kinetic  energy  in  each  organism  Selection 
is  constantly  operating  wherever  there  is  competition  with  the  correspond- 
ing actions,  reactions,  and  interactions  of  other  organisms. 

This  principle  I  shall  put  forth  in  different  aspects  as  the  central 
thought  of  these  lectures,  stating  at  the  outset  and  often  recurring 
to  the  admission  that  it  involves  several  unknown  principles  and 
especially  the  largely  hypothetical  question  whether  there  is  a  relation 
between  the  action,  reaction,  and  interaction  of  the  internal  energies 
of  the  germ  or  heredity-chromatin  with  the  external  energies  of  the 
inorganic  environment,  of  the  developing  organism,  and  of  its  life 
environment.  In  other  words,  while  this  is  a  principle  which  largely 
governs  the  Organism,  it  remains  to  be  discovered  whether  it  also 
governs  the  causes  of  the  Evolution  of  the  Germ. 

As  observed  in  the  preface  we  are  studying  not  one  but  four 
simultaneous  evolutions.  Each  of  these  evolutions  appears  to  be 
almost  infinite  in  itself  as  soon  as  we  can  examine  it  in  detail,  but  of 
the  four  that  of  the  germ  or  heredity-chromatin  so  far  surpasses  all 
the  others  in  complexity  that  it  appears  to  us  infinite. 

The  physicochemical  relations  between  these  four  evolutions, 
including  the  activities  of  the  single  and  of  the  multiplying  organisms 
of  the  Life  Environment,  may  be  expressed  in  diagrammatic  form  as 
follows : 


THE  TETRAKINETIC  THEORY 


283 


Organism  A 

Under 
Newtoti's  Laws  of  Motion 

and 
Modern  Thermodynamics 

Actions,  Reactions,  and 

Interactions 

of  the 

1 .  InorganicEnvironmetit: 

physicochemical  en- 
ergies of  space,  of  the 
sun,  earth,  air,  and 
water. 

2.  Organism,: 

physicochemical  en- 
ergies of  the  devel- 
oping individual  in 
the  tissues,  cells, 
protoplasm,  and  cell- 
chromatin. 

3.  Heredity-Germ: 

physicochemical  en- 
ergies of  the  heredity- 
chro matin  included 
in  the  reproductive 
cells  and  tissues. 

4.  Life  Environment: 

physicochemical  en- 
ergies of  other  or- 
ganisms. 


Under 

Darwin^ s  Law 

of 
Natural  Selection 

Survival  of  the  fittest: 
competition,  selec- 
tion, and  elimination 
of  the  energies  and 
forms. 


Organisms  B-Z 

Under 

Newton's  Laws  of  Motion 

and 

Modern  Thermodynamics 

Actions,  Reactions,  and 

Interactions 

of  the 

1.  InorganicEnvironmcnt: 

physicochemical  en- 
ergies of  space,  of  the 
sun,  earth,  air,  and 
water. 

2.  Organism: 

physicochemical  en- 
ergies of  the  devel- 
oping individual  in 
the  tissues,  cells, 
protoplasm,  and  ccU- 
chromatin. 

3.  IIcredity-Germ: 

physicochemical  en- 
ergies of  the  heredity- 
chromatin  included 
in  the  reproductive 
cells  and  tissues. 

4.  Life  Environment: 

physicochemical  en- 
ergies of  other  or- 
ganisms. 


If  a  single  name  is  demanded  for  this  conception  of  evolution  it 
might  be  termed  the  tetrakinetic  theory  in  reference  to  the  four  sets  of 
internal  and  external  energies  which  play  upon  and  within  every 
individual  and  every  race.  In  respect  to  form  it  is  a  tetraplastic 
theory  in  the  sense  that  every  living  plant  and  animal  form  is  plas- 
tically moulded  by  four  sets  of  energies.  The  derivation  of  this 
conception  of  life  and  of  the  possible  causes  of  evolution  from  the  laws 
which  have  been  developed  out  of  the  Newtonian  system,  and  from 
those  of  the  other  great  Cambridge  philosopher,  Charles  Darwin, 
are  clearly  shown  in  the  above  diagram. 


PART  IV 
GENETICS 


CHAPTER  XX 
THE  SCOPE  AND  METHODS  OF  GENETICS 

H.  H.  N. 
DEFINITIONS 

"  Genetics  is  the  science  which  seeks  to  account  for  the  resem- 
blances and  the  differences  which  are  exhibited  among  organisms 
related  by  descent." — Babcock  and  Clausen. 

"Genetics  may  be  defined  as  the  science  which  deals  with  the 
coming  into  being  of  organisms.  It  does  not  refer,  however,  to  the  first 
creation  of  organic  beings,  but  rather  to  the  present  every-day  creation 
of  new  individuals  or  new  races.  It  refers  particularly  to  the  part  that 
parent  organisms  have  in  bringing  new  organisms  into  being  and  to  the 
influence  which  parents  exert  on  the  characteristics  of  their  offspring. 
In  this  sense  it  is  nearly  equivalent  to  the  term  heredity.'' — W.  E. 
Castle. 

''Heredity  may  be  defined  as  organic  resemblance  based  on  de- 
scent."— W.  E.  Castle. 

''Heredity  is  commonly  defined  as  the  tendency  of  offspring  to 
develop  characters  like  those  of  the  parents." — Babcock  and  Clausen. 

THE    SCOPE   AND   METHODS   OF   GENETICS 

Genetics  is  the  study  of  evolution  from  a  new  point  of  view.  The 
great  evolutionists  of  the  past  were  devotees  of  the  inductive  method 
in  science  which  consists  of  collecting  data  and  devising  theories  to 
explain  the  data.  None  of  the  older  evolutionists  attempted  to  put 
their  theories  to  experimental  tests.  Thus  their  theories,  though  in 
some  respects  well  founded,  have  never  reached  that  stage  of  scientific 
proof  which  involves  the  use  of  the  experimental  method.  The  new 
method  in  evolution  is  that  of  experiment  under  controlled  conditions. 
If  new  characters  arise  before  the  eyes  of  the  investigator  in  a  known 
stock  of  animals  or  plants  and  the  factors  responsible  for  the  change 
are  known  and  are  capable  of  control,  it  may  be  said  that  man  has 
actually  taken  a  hand  in  evolution.  If  new  characters  arise  in  a 
known  stock,  but  from  an  unknown  cause,  the  course  of  the  new 
character  in  inheritance  may  be  controlled  and  some  knowledge  of  the 

287 


288     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

mechanism  of  heredity  may  be  obtained  by  an  analysis  of  its  modes  of 
heredity.  It  is  this  new  experimental  and  analytic  method  of  study- 
ing evolution  that  we  have  come  to  designate  as  genetics. 

Three  principal  methods  of  attack  upon  the  problems  of  genetics 
have  been  successful  in  advancing  our  knowledge. 

a)  Experimental  breeding. — This  method  was  first  systematized 
by  Mendel  and  consists  of  breeding  together  two  individuals  possessing 
certain  more  or  less  contrasting  characters  and  determining  the  ratios 
in  which  the  parental  characters  reappear  in  the  offspring.  This 
method  has  been  extremely  fruitful  and  in  connection  with  the  second 
method,  that  of  cytology,  has  made  clear  much  that  was  obscure  to 
Darwin  and  his  followers. 

b)  Cytology. — This  second  method  involves  the  microscopic 
study  of  the  germ  cells  during  the  most  critical  periods  of  their  cycle. 
It  seems  very  probable  that  we  can  now  view  under  the  microscope 
the  actual  heredity  machine  and  see  how  it  works. 

c)  The  statistical  method. — ^It  is  usually  conceded  that  Sir 
Francis  Galton  was  the  first  to  use  the  method  of  statistics  in  the  study 
of  heredity.  By  means  of  correlation  tables  he  was  able  to  compare 
large  groups  of  parents  with  large  groups  of  offspring  with  respect  to 
any  unit  character,  and  to  state  the  degree  of  heredity  in  defin- 
ite mathematical  terms.  The  modern  science  of  biometry  is  used 
extensively  at  the  present  time  for  determining  the  degree  of  vari- 
ability of  characters  which  vary  only  slightly  or  irregularly  and  the 
exact  degree  of  correlation  that  exists  between  different  hereditary 
characters. 

All  three  of  these  methods  of  attacking  the  problems  of  genetics 
have  been  fruitful  in  results  and  all  are  essential  to  an  adequate  under- 
standing of  the  workings  of  evolution. 

The  subject-matter  of  genetics  consists  of:  {a)  a  knowledge  of  the 
principles  of  ontogeny,  the  development  of  the  individual  from  the 
germ-cell  stage  to  the  adult  stage;  {h)  a  knowledge  of  the  behavior  of 
the  germ  cells  from  one  generation  to  the  next,  involving  the  so-called 
"origin"  of  germ  cells,  maturation  and  fertilization  of  germ  cells,  and 
the  exact  behavior  of  the  chromosomes  during  the  entire  germ-cell 
cycle;  (c)  a  knowledge  of  variation,  including  a  determination  of 
what  distinct  kinds  of  variation  occur,  where  in  ontogeny  variations 
are  initiated,  the  causes  of  variation,  etc. ;  {d)  what  kinds  of  variations 
are  inherited  and  according  to  what  laws — the  whole  subject  of  Men- 
delian  heredity;   {e)  the  determination  of  sex  and  the  relation  of 'sex 


THE  SCOPE  AND  METHODS  OF  GENETICS  289 

to  heredity;  (/)  theories  as  to  the  mechanism  that  brings  about  the 
observed  regularity  in  heredity,  including  theories  of  linkage,  cross- 
overs, and  other  phases  of  neo-Mendelian  heredity. 

THE   IMPORTANCE   OF   THE   CELL   THEORY   IN   GENETICS 

All  organisms  are  composed  of  minute  units  called  cells.  A  cell 
is  the  smallest  particle  of  living  matter  capable  of  growing  and  multi- 
plying. The  only  continuity  between  two  successive  generations  is  a 
cellular  continuity,  involving  a  continuous  series  of  cell  divisions. 
All  cells  are  the  offspring  by  division  of  previous  cells.  We  distinguish 
two  main  categories  of  cells:   body  or  somatic  cells  and  germ  cells. 

In  germinal  reproduction,  the  only  kind  of  reproduction  possible 
in  the  more  highly  differential  animals,  the  material  continuity 
between  parent  and  offspring  is  through  the  germ  cell.  A  parental 
germ  cell  produces  an  offspring.  The  germ  cell  therefore  is  called  the 
hereditary  bridge. 

The  only  way,  then,  in  which  a  parent  can  transmit  his  or  her 
characteristics  to  an  offspring  is  through  the  germ  cell.  Every 
hereditary  character,  whether  old  or  new,  must  have  its  differential 
cause  in  the  germ  cell.  The  germ  cells  are  therefore  called  the  bearers 
of  the  heritage,  and  in  the  next  chapter  Professor  M.  F.  Guyer  gives 
an  account  of  the  cellular  basis  of  variation  and  heredity. 


CHAPTER  XXI 

THE  BEARERS  OF  THE  HERITAGE 
AN  ACCOUNT  OF  THE  CELLULAR  BASIS  OF  HEREDITY^ 

MICHAEL    F.    GUYER 

Structure  of  the  cell. — Before  we  can  understand  certain  necessary- 
details  of  the  physical  mechanism  of  inheritance  we  must  inquire  a 
little  further  into  the  finer  structure  of  the  cell  and  into  the  nature 
of  cell-division.  A  typical  cell,  as  it  would  appear  after  treatment 
with  various  stains  which  bring  out  the  different  parts  more  dis- 
tinctly, is  shown  in  Fig.  43.  Typical,  not  that  any  particular  kind  of 
living  cell  resembles  it  very  closely  in  appearance,  but  because  it  shows 
in  a  diagrammatic  way  the  essential  parts  of  a  cell.  In  the  diagram, 
there  are  two  well-marked  regions :  a  central  nucleus  and  a  peripheral 
cell-body  or  cytoplasm.  Other  structures  are  pictured,  but  only  a  few 
of  them  need  command  our  attention  at  present.  At  one  side  of  the 
nucleus  one  observes  a  small  dot  or  granule  surrounded  by  a  denser 
area  of  cytoplasm.  This  body  is  called  the  centrosome.  The  nucleus 
in  this  instance  is  bounded  by  a  well-marked  nuclear  membrane  and 
within  it  are  several  substances.  What  appear  to  be  threads  of  a 
faintly  staining  material,  the  linin,  traverse  it  in  every  direction  and 
form  an  apparent  network.  The  parts  on  which  we  wish  particularly 
to  rivet  our  attention  are  the  densely  stained  substances  scattered  along 
or  imbedded  in  the  strands  of  this  network  in  irregular  granules  and 
patches.  This  substance  is  called  chromatin.  It  takes  its  name  from 
the  fact  that  it  shows  great  affinity  for  certain  stains  and  becomes 
intensely  colored  by  them.  This  deeply  colored  portion  of  the  cell, 
the  chromatin,  is  by  most  biologists  regarded  as  of  great  importance 
from  the  standpoint  of  heredity.  One  or  more  larger  masses  of 
chromatin  or  chromatin-like  material,  known  as  chromatin  nucleoli, 
are  often  present,  and  not  infrequently  a  small  spheroidal  body, 
differing  in  its  staining  reactions  from  the  chromatin-nucleolus  and 
sometimes  called  the  true  nucleolus,  exists. 

Cell-division. — In  the  simplest  type  of  cell-division  the  nucleus 
first  constricts  in  the  middle,  and  finally  the  two  halves  separate. 

*  From  M.  F.  Guyer,  Being  Well  Born  (copyright  19 16).  Used  by  special 
permission  of  the  publishers,  The  Bobbs-Merrill  Company. 

290 


THE  BEARERS  OF  THE  HERITAGE 


291 


This  separation  is  followed  by  a  similar  constriction  and  final  division 
of  the  entire  cell-body,  which  results  in  the  production  of  two  new 
cells.  This  form  of  cell-division  is  known  as  s'wiple  or  direct  dimsion. 
Such  a  simple  division,  while  found  in  higher  animals,  is  less  frequent 
and  apparently  much  less  significant  than  another  type  of  division 
which  involves  profound  changes  and  rearrangements  of  the  nuclear 
contents.  The  latter  is  termed  mitotic  or  indirect  cell-division.  Fig.  44 
illustrates  some  of  the  stages  which  are  passed  through  in  indirect 
cell-division.  The  centrosome  which  lies  passively  at  the  side  of  the 
nucleus  in  the  typical  cell  (Fig.  44,  a)  awakens  to  activity,  divides  and 
the  two  components  come  to  lie  at  the  ends  of  a  fibrous  spindle.     In 

Centrosome. 


■Nucleus. 


Chromatin.  - — 

Triie 

nucleolus 
(plasmosome). 

Chromatin   »— 
nucleolus. 

Linin    — 
network. 


1 _-j>  P last  ids. 


V 


Vacuole. 
Aletaf'lasnt 
(passne  buiies). 


Fig.  43. — Diagram  of  a  cell,  showing  various  parts.     {From  Guyer.) 


the  meantime,  the  interior  of  the  nucleus  is  undergoing  a  transforma- 
tion. The  granules  and  patches  of  chromatin  begin  to  flow  together 
along  the  nuclear  network  and  become  more  and  more  crowded 
until  they  take  on  the  appearance  of  one  or  more  long  deepl\'- 
stained  threads  wound  back  and  forth  in  a  loose  skein  in  the  nucleus 
(Fig.  44,  b).  If  we  examine  this  thread  closely,  in  some  forms  it  may 
be  seen  to  consist  of  a  series  of  deeply-stained  chromatin  granules 
packed  closely  together,  intermingled  with  the  substance  of  the 
original  nuclear  network. 

As  the  preparations  for  division  go  on  the  coil  in  the  nucleus  breaks 
up  into  a  number  of  segments  which  are  designated  as  chromosomes 
(Fig.  44,  c).     The  nuclear  membrane  disappears.     The  chromosomes 


292     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 


and  the  spindle-fibers  ultimately  come  to  lie  at  the  equator  of  the 
spindle  as  shown  in  Fig.  44,  d.  Each  chromosome  splits  lengthwise 
to  form  two  daughter  chromosomes  which  then  diverge  to  pass  to  the 


mss 


Fig.  44. — Diagram  showing  representative  stages  in  mitotic  or  indirect  cell- 
di\dsion.  a,  resting  cell  with  reticular  nucleus  and  single  centrosome;  h,  the 
two  new  centrosomes  formed  by  division  of  the  old  one  are  separating  and  the 
nucleus  is  in  the  spireme  stage;  c,  the  nuclear  wall  has  disappeared,  the  spireme 
has  broken  up  into  six  separate  chromosomes,  and  the  spindle  is  forming  between 
the  two  centrosomes;  J,  equatorial  plate  stage  in  which  the  chromosomes  occupy 
the  equator  of  the  spindle;  e,f,  each  chromosome  splits  lengthwise  and  the  daughter 
chromosomes  thus  formed  approach  their  respective  poles;  g,  reconstruction  of 
the  new  nuclei  and  division  of  the  cell  body;  h,  cell  division  completed.  {From 
Qiiyer.) 


poles  of  the  spindle  (Fig.  44,  e  and/).  Thus  each  end  of  the  spindle 
comes  ultimately  to  be  occupied  by  a  set  of  chromosomes.  Moreover, 
each  set  is  a  duplicate  of  the  other,  because  the  substance  of  any 
individual  chromosome  in  one  group  has  its  counterpart  in  the  other. 


THE  BEARERS  OF  THE  HERITAGE  293 

In  fact  this  whole  complicated  system  of  indirect  division  is  regarded 
by  most  biologists  as  a  mechanism  for  bringing  about  the  precise 
halving  of  the  chromosomes. 

The  chromosomes  of  each  group  at  the  poles  finally  fuse  and  two 
new  nuclei,  each  similar  to  the  original  one,  are  constructed  (Fig.  44, 
g  and  h).  In  the  meantime  a  division  of  the  cell-body  is  in  progress 
which,  when  completed,  results  in  the  formation  of  two  complete 
new  cells. 

As  all  living  matter,  if  given  suitable  food,  can  convert  it  into  living 
matter  of  its  own  kind,  there  is  no  difficulty  in  conceiving  how  the 
new  cell  or  the  chromatin  material  finally  attains  to  the  same  bulk 
that  was  characteristic  of  the  parent  cell.  In  the  case  of  the  chro- 
matin, indeed,  it  seems  that  there  is  at  times  a  precocious  doubling 
of  the  ordinary  amount  of  material  before  the  actual  division 
occurs. 

Chromosomes  constant  in  number  and  appearance. — With  some 
minor  exceptions,  to  be  noted  later,  which  increase  rather  than  detract 
from  the  significance  of  the  facts,  the  chromosomes  are  always  the 
same  in  number  and  appearance  in  all  individuals  of  a  given  species 
of  plants  or  animals.  That  is,  every  species  has  a  fixed  number  which 
regularly  recurs  in  all  of  its  cell-divisions.  Thus  the  ordinary  cells 
of  the  rat,  when  preparing  to  divide,  each  display  sixteen  chromo- 
somes, the  frog  or  the  mouse,  twenty-four,  the  lily  twenty-four  and 
the  maw- worm  of  the  horse  only  four.  The  chromosomes  of  dififerent 
kinds  of  animals  or  plants  may  differ  very  much  in  appearance.  In 
some  they  are  spherical,  in  others  rod-like,  filamentous  or  perhaps  of 
other  forms.  In  some  organisms  the  chromosomes  of  the  same  nucleus 
may  differ  from  one  another  in  size,  shape,  and  proportions,  but  if  such 
differences  appear  at  one  division  they  appear  at  others,  thus  showing 
that  in  such  cases  the  differences  are  constant  from  one  generation  to 
the  next. 

Significance  of  the  chromosomes. — The  question  naturally  arises 
as  to  what  is  the  significance  of  the  chromosomes.  Why  is  the  accur- 
ate adjustment  which  we  have  noted  for  their  division  necessary  ? 
The  very  existence  of  an  elaborate  mechanism  so  admirably  adapted 
to  their  precise  halving,  predisposes  one  toward  the  belief  that  the 
chromosomes  have  an  important  function  which  necessitates  the 
retention  of  their  individuality  and  their  equal  division.  Many  biolo- 
gists accept  this  along  with  other  evidences  as  indicating  that  in 
chromatin  we  have  a  substance  which  is  not  the  same  throughout,  that 


294     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

different  regions  of  the  same  chromosome  have  different  physiological 
values. 

When  the  cell  prepares  for  divisions,  the  granules,  as  we  have 
seen,  arrange  themselves  serially  into  a  definite  number  of  strands 
which  we  have  termed  chromosomes.  Judging  from  all  available 
evidence,  the  granules  are  self-propagating  units;  this  is,  they  can 
grow  and  reproduce  themselves.  So  that  what  really  happens  in  mito- 
sis in  the  splitting  of  the  chromosomes  is  a  precise  halving  of  the  series 
of  individual  granules  of  which  each  chromosome  is  constituted,  or  in 
other  words  each  granule  has  reproduced  itself.  Thus  each  of  the  two 
daughter  cells  presumably  gets  a  sample  of  every  kind  of  chromosomal 
particle,  hence,  the  two  cells  are  qualitatively  alike.  To  use  a  homely 
illustration  we  may  picture  the  individual  chromosomes  to  ourselves 
as  so  many  separate  trains  of  freight  cars,  each  car  of  which  is  loaded 
with  different  merchandise.  Now,  if  every  one  of  the  trains  could 
split  along  its  entire  length  and  the  resulting  halves  each  grow  into  a 
train  similar  to  the  original,  so  that  instead  of  one  there  would  exist 
two  identical  trains,  we  should  have  a  phenomenon  analogous  to  that 
of  a  dividmg  chromosome. 

Cleavage  of  the  egg. — It  is  through  a  series  of  such  divisions  as 
these  that  the  zygote  or  fertilized  egg-cell  builds  up  the  tissues  and 
organs  of  the  new  organism.  The  process  is  technically  spoken  of  as 
cleavage.  Cleavage  generally  begins  very  shortly  after  fertilization. 
The  fertile  egg-cell  divides  into  two,  the  resulting  cells  divide  again  and 
thus  the  process  continues,  with  an  ever-increasing  number  of  cells. 

Chief  processes  operative  in  building  the  body. — Although  of 
much  interest,  space  will  not  permit  of  a  discussion  in  detail  of  the 
building  up  of  the  special  organs  and  tissues  of  the  body.  It  must 
suffice  merely  to  mention  the  four  chief  processes  which  are  operative. 
These  are,  (i)  infoldings  and  outfoldings  of  the  various  cell  com- 
plexes; (2)  multiplication  of  the  component  cells;  (3)  special  changes 
{histological  diferentiation)  in  groups  of  cells;  and  (4)  occasionally 
resorption  of  certain  areas  of  parts. 

The  origin  of  the  new  germ-cells. — On  account  of  the  unusual 
importance  from  the  standpoint  of  inheritance,  which  attaches  to  the 
germ-cells,  a  final  word  must  be  said  about  their  origin  in  the  embryo. 
While  the  evidence  is  conflicting  in  some  cases,  in  others  it  has  been 
well  established  that  the  germ-cells  are  set  apart  very  early  from  the 
cells  which  are  to  differentiate  into  the  ordinary  body  tissues.  Fig.  45, 
A,  shows  a  section  through  the  eight-celled  stage  of  Miastor,  a  fly. 


THE  BEARERS  OF  THE  HERITAGE  295 

in  which  a  single  large,  primordial  germ-cell  (/>.  g.  c.)  has  already  been 
set  apart  at  one  end  of  the  developing  embryo.  The  nuclei  of  the  rest 
of  the  embryo  still  lie  in  a  continuous  protoplasmic  mass  which  has 
not  yet  divided  up  into  separate  cells.  The  densely  stainerl  nuclei  at 
the  opposite  end  of  the  section  are  the  remnants  of  nurse-cells  which 
originally  nourished  the  tgg.     Fig.  45,  B,  is  a  longitudinal  section 


o'6  g 


Fig.  45. — A,  germ-cell  (p.g.c.)  set  apart  in  the  eight-celled  stage  of  cleavage 
in  Miastor  americana.  {After  Hegner.)  The  walls  of  the  remaining  seven  somatic 
cells  have  not  yet  formed,  though  the  resting  or  the  dividing  {M  p)  nuclei  may  be 
seen;  c  R,  chromatin  fragments  cast  off  from  the  somatic  cells;  B,  section  length- 
wise of  a  later  embryo  of  Miastor;  the  primordial  egg-cells  (odgj)  are  conspicuous. 
{From  Guyer,  after  Hegner.) 


through  a  later  stage  in  the  development  of  Miastor;  the  primitive 
germ-cells  (oog)  are  plainly  visible.  Still  other  striking  examples 
might  be  cited.  Even  in  vertebrates  the  germ-cells  may  often  be 
detected  at  a  very  early  period. 

Significance  of  the  early  setting  apart  of  the  germ-cells.  —It  is 
of  great  importance  for  the  reader  to  grasp  the  significance  of  this 
early  setting  apart  of  the  germ-cells  because  so  much  in  our  future 
hinges  on  this  fact.  The  truth  of  the  statement  made  in  a  previous 
chapter  that  the  body  of  an  individual  and  the  reproductive  substance 


296     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

in  that  body  are  not  identical  now  becomes  obvious.  For  in  such 
cases  as  those  just  cited  one  sees  the  germinal  substance  which  is  to 
carry  on  the  race  set  aside  at  an  early  period  in  a  given  individual;  it 
takes  no  part  in  the  formation  of  that  individual's  body,  but  remains 
a  slumbering  mass  of  potentialities  which  must  bide  its  time  to  awaken 
into  expression  in  a  subsequent  generation.  Thus  an  egg  does  not 
develop  into  a  body  which  in  turn  makes  new  germ-cells,  but  body  and 
germ-cells  are  established  at  the  same  time,  the  body  harboring  and 
nourishing  the  germ-cells,  but  not  generating  them.  The  same  must 
be  true  also  in  many  cases  where  the  earliest  history  of  the  germ-cells 
cannot  be  visibly  followed,  because  in  any  event,  in  all  higher  animals, 
they  appear  long  before  the  embryo  is  mature  and  must  therefore  be 
descendants  of  the  original  egg-cell  and  not  of  the  functioning  tissues 
of  the  mature  individual.  This  need  not  necessarily  mean  that  the 
germ-cells  have  remained  wholly  unmodified  or  that  they  continue 
uninfluenced  by  the  conditions  which  prevail  in  the  body,  especially 
in  the  nutritive  blood  and  lymph  stream,  although  as  a  matter  of  fact 
most  biologists  are  extremely  skeptical  as  to  the  probability  that 
influences  from  the  body  beyond  such  general  indefinite  effects  as 
might  result  from  under-nutrition  or  from  poisons  carried  in  the  blood, 
modify  the  intrinsic  nature  of  the  germinal  substances  to  any  measur- 
able extent. 

Germinal  continuity. — The  germ-cells  are  collectively  termed  the 
germinal  protoplasm  and  it  is  obvious  that  as  long  as  any  race  continues 
to  exist,  although  successive  individuals  die,  some  germinal  protoplasm 
is  handed  on  from  generation  to  generation  without  interruption. 
This  is  known  as  the  theory  of  germinal  continuity.  When  the  organ- 
ism is  ready  to  reproduce  its  kind  the  germ-cells  awaken  to  activity, 
usually  undergoing  a  period  of  multiplication  to  form  more  germ-cells 
before  finally  passing  through  a  process  of  what  is  known  as  matura- 
tion^ which  makes  them  ready  for  fertilization.  The  maturation 
process  proper,  which  consists  typically  of  two  rapidly  succeeding 
divisions,  is  preceded  by  a  marked  growth  in  size  of  the  individual  cells. 

Individuality  of  chromosomes. — Before  we  can  understand  fully 
the  significance  of  the  changes  which  go  on  during  maturation  we  shall 
have  to  know  more  about  the  conditions  which  prevail  among  the 
chromosomes  of  cells.  As  already  noted  each  kind  of  animal  or  plant 
has  its  own  characteristic  number  and  types  of  chromosomes  when 
these  appear  for  division  by  mitosis.  In  many  organisms  the  chromo- 
somes are  so  nearly  of  one  size  as  to  make  it  difficult  or  impossible  to 


THE  BEARERS  OF  THE  HERITAGE  297 

be  sure  of  the  identity  of  each  individual  chromosome,  but  on  the 
other  hand,  there  are  some  organisms  known  in  which  the  chromo- 
somes of  a  single  nucleus  are  not  of  the  same  size  and  form  (Fig.  46). 
These  latter  cases  enable  us  to  determine  some  very  significant  facts. 
Where  such  differences  of  shape  and  proportion  occur  they  are  constant 
in  each  succeeding  division  so  that  similar  chromosomes  may  be  iden- 
tified each  time.  Moreover,  in  all  ordinary  mitotic  divisions  where 
the  conditions  are  accurately  known,  these  chromosomes  of  ditTcrent 
types  are  found  to  be  present  as  pairs  of  similar  elements;  that  is, 
there  are  two  of  each  form  or  size. 

Pairs  of  similar  chromosomes  in  the  nucleus  because  one  chromo- 
some comes  from  each  parent— When  we  recall  that  the  original 
fertilized  egg  from  which  the  individual  develops  is  really  formed  by 
the  union  of  two  gametes,  ovum  and  spermatozoon,  and  that  each 


B 

Fig.  46. — A,  chromosomes  of  the  mosquito  (Culex).  (After  Stevens.)  B, 
chromosomes  of  the  fruit  fly  (Drosophila).  (After  Metz.)  Both  of  these  forms 
have  an  unusually  small  number  of  chromosomes.     (From  Guyer.) 

gamete,  being  a  true  cell,  must  carry  its  own  set  of  chromosomes,  the 
significance  of  the  pairs  of  similar  chromosomes  becomes  evident;  one 
of  each  kind  has  probably  been  contributed  by  each  gamete.  This 
means  that  the  zygote  or  fertile  ovum  contains  double  the  number  of 
chromosomes  possessed  by  either  gamete,  and  that,  moreover,  each 
tissue-cell  of  the  new  individual  will  contain  this  dual  number.  For, 
as  we  have  seen,  the  number  of  chromosomes  is,  with  possibly  a  few 
exceptions,  constant  in  the  tissue-cells  and  early  germ-cells  in  suc- 
cessive generations  of  individuals.  For  this  to  be  true  it  is  obvious 
that  in  some  way  the  nuclei  of  the  conjugating  gametes  have  come  to 
contain  only  half  the  usual  number.  Technically  the  tissue-cells  are 
said  to  contain  the  diploid  number  of  chromosomes,  the  gametes  the 
reduced  or  haploid  number. 

In  maturation  the  number  of  chromosomes  is  reduced  by  one- 
half. — This  halving,  or  as  it  is  known,  reduction  in  the  number  of 
chromosomes  is  the  essential  feature  of  the  process  of  maturation.     It 


298      READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

is  accomplished  by  a  modification  in  the  mitotic  division  in  which 
instead  of  each  chromosome  spHtting  lengthwise,  as  in  ordinary  mito- 
sis, the  chromosomes  unite  in  pairs  (Fig.  47,  b),  a  process  known  tech- 
nically as  synapsis,  and  then  apparently  one  member  of  each  pair  passes 
entire  into  one  new  daughter  cell,  the  other  member  going  to  the  other 
daughter  cell  (Fig.  47,  c).  In  the  pairing  preliminary  to  this  reduction 
division,  leaving  out  of  account  certain  special  cases  to  be  considered 


Fig.  47. — Diagram  to  illustrate  spermatogenesis,  a,  showing  the  diploid 
number  of  chromosomes  (six  is  arbitrarily  chosen)  as  they  occur  in  divisions  of 
ordinary  cells  and  spermatogonia;  h,  the  pairing  (synapsis)  of  corresponding 
mates  in  the  primary  spermatocyte  preparatory  to  reduction;  c,  each  secondary 
spermatocyte  receives  three,  the  haploid  number  of  chromosomes;  d,  division  of 
the  secondary  spermatocytes  to  form  e,  spermatids,  which  transform  into  /,  sper- 
matozoa.    {From  Guyer.) 


later,  according  to  the  best  evidence  at  our  command  the  union  always 
takes  place  between  two  chromosomes  which  match  each  other  in  size 
and  appearance.  Since  one  of  these  is  believed  to  be  of  maternal  and 
the  other  of  paternal  origin,  the  ensuing  division  separates  correspond- 
ing mates  and  insures  that  each  gamete  gets  one  of  each  kind  of  chro- 
mosome although  it  appears  to  be  a  matter  of  mere  chance  whether  or 
not  a  given  cell  gets  the  paternal  or  the  maternal  representative  of 
that  kind. 


THE  BEARERS  OF  THE  HERITAGE 


299 


Maturation  of  the  sperm-cell.— In  the  maturation  of  the  male 
gamete  the  germ-cell,  now  known  as  a  spermalogoniion,  increases 
greatly  in  size  to  become  a  primary  spermatocyte.  In  each  primary 
spermatocyte  the  pairing  of  the  chromosomes  already  alluded  to 
occurs  as  indicated  in  Fig.  47,  where  six  is  taken  arbitrarily  to  indicate 
the  ordinary  or  diploid  number  of  chromosomes,  and  three  the  reduced 
or  haploid  number.  The  division  of  the  primary  spermatocyte  gives 
rise  to  two  secondary  spermatocytes  {c),  the  i)aired  chromosomes 
separating  in  such  a  way  that  a  member  of  each  pair  goes  to  each 


Fig.  48. — Diagram  to  illustrate  oogenesis,  a,  showing  the  diploid  number  of 
chromosomes  (six  is  arbitrarily  chosen)  as  they  occur  in  ordinary  cells  and  in 
oogonia;  6,  the  pairing  of  corresponding  mates  preparatory  to  reduction;  r.  d, 
the  reduction  division,  giving  off  the  first  polar  body;  e,  egg  preparing  to  give  off  the 
second  polar  body,  first  polar  body  ready  for  division;  /,  second  polar  body  ready 
for  division;  g,  second  polar  body  given  off,  division  of  first  polar  body  completed. 
The  egg  nucleus,  now  known  as  the  female  pronucleus,  and  each  polar  body  contain 
the  reduced  or  haploid  number  of  chromosomes.     {From  Guycr.) 


secondary  spermatocyte.  Each  secondary  spermatocyte  {d)  soon 
divides  again  into  two  spermatids  (e),  but  in  this  second  division  the 
chromosomes  each  split  lengthwise  as  in  an  ordinary  division  so  that 
there  is  no  further  reduction.  In  some  forms  the  reduction  division 
occurs  in  the  secondary  spermatocytes  instead  of  the  primar\'.  Kach 
spermatid  transforms  into  a  mature  spermatozoon  (/).  The  sper- 
matozoa of  most  animals  are  of  linear  form,  each  with  a  head,  a 
middle-piece  and  a  long  vibratile  tail  which  is  used  for  locomotion. 
The  head  consists  for  the  most  part  of  the  transformed  nucleus  and  is 
consequently  the  part  which  bears  the  chromosomes. 


300     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

Maturation  of  the  egg-cell. — As  regards  the  behavior  of  the 
chromosomes  the  maturation  of  the  ovum  parallels  that  of  the  sperm- 
cell.  There  are  not  so  many  primordial  germ-cells  formed  and  only 
one  out  of  four  of  the  ultimate  cells  becomes  a  functional  egg.  As  in 
maturation  of  the  sperm-cell  there  is  a  growth  period  in  which  oogonia 
enlarge  to  become  primary  oocytes  (Fig.  48,  b).     In  each  primary 


Spermatogenesis 


Oogenesis 

i 


gofiia         \^'^ 


MulltpliCQlion  Period . 


t  \ 


J>/Jm9rv..   fAt^  1 


ipermocpc  i/te     V  n^  »/ ' 


CroMth  period 


Pairing  of  Chromosomes 


©•'       '% 


\      }  Re<^ucing  division 


Secanaory  ( ^ 
J  per  mot  o-  '     " 
ei/ttj 


Sperm  f  <' 


Saerm 
eRozoa 


Obgonio 


.-■■  s 


Primori^  C80/l^^ 


Seconc/ari/  odcytt 
fpyufTi  and  ftrsl 
^  polar  bo&jf) 


/loture  ofufoy  , 
anc/ ptior  bt^itj. 


©nature  oyum\ 


full  number  of 
Chromoiomti 
restored 


Z  If  gate  or 
Jeriiliztd 
ovum 


Fig.  49. — Diagram  showing  the  parallel  between  maturation  of  the  sperm- 
cell  and  maturation  of  the  ovum.     {From  Guyer.) 


oocyte  as  in  the  primary  spermatocyte  the  chromosomes  pair  and  two 
rapidly  succeeding  divisions  follow  in  one  of  which  the  typical  numeri- 
cal reduction  in  the  chromosomes  occurs.  A  peculiarity  in  the 
maturation  of  the  ovum  is  that  there  is  a  very  unequal  division  in 
the  cytoplasm  in  cell-division  so  that  three  of  the  resulting  cells 
usually  termed  polar  bodies  are  very  small  and  appear  like  minute 
buds  on  the  side  of  the  fourth  or  egg-cell  proper. 


THE  BEARERS  OF  THE  HERITAGE  301 

The  scheme  of  this  formation  of  the  polar  bodies  is  indicated  in 
Fig.  48.  In  Fig.  48,  b  the  chromosomes  are  seen  paired  and  ready  for 
the  first  division;  that  is,  for  the  formation  of  the  first  polar  body. 
Figs.  48,  c,  d  show  the  giving  off  of  this  body.  Note  that  while  only  a 
small  proportion  of  the  cytoplasm  passes  into  this  tiny  cell,  its  chro- 
matin content  is  as  great  as  that  of  the  ovum.  A  second  polar  body 
(Fig.  48,  e)  is  formed  by  the  egg,  but  in  this  case  each  chromosome 
spHts  lengthwise,  as  in  ordinary  mitosis,  and  there  is  no  further  numeri- 
cal reduction.  In  the  meantime,  typically,  a  third  polar  bo(h-  is 
formed  by  division  of  the  first.    (Stages  e,  /,  g.) 

Parallel  between  the  maturation  of  sperm-  and  egg-cell. — This 
rather  complex  procedure  of  the  germ-cells  will  be  rendered  more 
intelHgible  through  a  careful  study  of  Figs.  47,  48,  and  49,  which 
indicates  the  parallel  conditions  in  spermatogenesis  and  oogenesis. 

The  view  now  generally  held  regarding  the  polar  bodies  is  that  they 
are  really  abortive  eggs.  They  later  disappear,  taking  no  part  in 
embryo-formation.  It  can  readily  be  seen  how  such  an  unequal 
division  is  advantageous  to  the  large  cell,  for  it  receives  all  of  the  rich 
store  of  food  material  that  would  be  distributed  among  the  four  cells 
if  all  were  of  equal  size.  This  increased  amount  of  food  is  a  favorable 
provision  for  the  forthcoming  offspring  whose  nourishment  is  thus 
more  thoroughly  insured. 

On  the  other  hand,  all  of  the  sperm-cells  develop  int3  complete 
active  forms,  which,  as  aforesaid,  usually  become  very  much  elongated 
and  develop  a  motile  organ  of  some  kind.  In  such  cells  an  accumula- 
tion of  food  to  any  large  extent  would  hinder  rather  than  help  them, 
because  it  would  seriously  interfere  with  their  activity. 

Fertilization. — In  fertilization  (Fig.  50)  the  spermatozoon  pene- 
trates the  wall  of  the  ovum  and  after  undergoing  considerable  altera- 
tion its  nucleus  fuses  with  the  nucleus  of  the  egg.  In  some  forms 
only  the  head  (nucleus)  and  middle-piece  enter,  the  tail  being  cut  off 
by  a  so-called  fertilization  membrane  which  forms  at  the  surface  of 
the  egg  and  effectually  blocks  the  entrance  of  other  spermatozoa. 
Thus  normally  only  one  spermatozoon  unites  with  an  egg.  In  some 
forms  while  several  may  enter  the  egg  only  one  becomes  functional. 
As  soon  as  the  nucleus  of  the  spermatozoon,  now  known  as  the  ffuile 
pronucleus,  reaches  the  interior  of  the  egg,  it  enlarges  and  becomes  simi- 
lar in  appearance  to  the  female  pronucleus.  It  swings  around  in  such 
a  way  (Fig.  50,  b)  that  the  middle  piece,  now  transformed  into  a  centro- 
some,  lies  between  it  and  the  female  pronucleus.     The  two  pronuclei 


302      READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 


{c,  d,  e) ,  each  containing  the  reduced  number  of  chromosomes,  approach, 
the  centrosome  divides,  the  nuclear  walls  disappear,  the  typical 
division  spindle  forms,  and  the  chromosomes  of  paternal  and  maternal 
origin  respectively  come  to  lie  side  by  side  at  the  equator  of  the  spindle 
ready  for  the  first  division  or  cleavage  (/,  g).     It  will  be  noted  that  the 


Fig.  50. — Diagram  to  illustrate  fertilization;  $,  male  pronucleus;  ?,  female 
pronucleus;  observe  that  the  chromosomes  of  maternal  and  paternal  origin 
respectiv^ely  do  not  fuse.     {From  Giiyer.) 


individual  chromosomes  do  not  intermingle  their  substance  at  this 
time,  but  each  apparently  retains  its  own  individuality.  There  is 
considerable  evidence  which  indicates  that  throughout  life  the  chro- 
mosomes contributed  by  the  male  parent  remain  distinct  from  those 
of  the  female  parent.  Inasmuch  as  each  germ-cell,  after  maturation, 
contains  only  half  the  characteristic  number  of  chromosomes,  the 
original  number  is  restored  in  fertilization. 

Significance   of  the   behavior   of   chromosomes. — The   question 
confronts  us  as  to  what  is  the  significance  of  this  elaborate  system 


THE  BEARERS  OF  THE  HERITAGE  303 

which  keeps  the  chromosomes  of  constant  size,  shape  and  number; 
which  partitions  them  so  accurately  in  ordinary  cell-division; 
and  which  provides  for  a  reduction  of  their  numbers  by  half  in  the 
germ-cell  while  yet  securing  that  each  mature  gamete  gets  one  of  each 
kind  of  chromosome.  Most  biologists  look  on  these  facts  i.s  indicating 
that  the  chromosomes  are  specifically  concerned  in  inheritance. 

In  the  first  place  it  is  recognized  that  as  regards  the  definable 
characters  which  separate  individuals  of  the  same  species,  offspring 
may  inherit  equally  from  either  parent.  And  it  is  a  very  significant 
fact  that  while  the  ovum  and  spermatozoon  are  very  unequal  in  size 
themselves,  the  chromosomes  of  .he  two  germ-cells  are  of  th^  same 
size  and  number.  This  parity  in  chromosomal  contributi  )n  points 
clearly  to  the  means  by  which  an  equal  number  of  character  deter- 
miners might  be  conveyed  from  each  parent.  Moreover  it  is  mainly 
the  nucleus  of  the  sperm-cell  in  some  organisms  which  enters  the  egg, 
hence  the  determiners  from  the  male  line  must  exist  wholly  or  largely 
somewhere  in  the  nucleus.  And  the  bulk  of  the  nucleus  in  the  sper- 
matozoon consists  of  the  chromosomes  or  their  products. 

A  single  set  of  chromosomes  derived  from  one  parent  only  is 
sufficient  for  the  production  of  a  complete  organism. — That  a  single 
or  haploid  set  of  chromosomes  as  seen  in  the  gametes  is  sufficient 
contribution  of  chromatin  for  the  production  of  a  complete  organism 
is  proved  by  the  fact  that  the  unfertilized  eggs  of  various  animals 
(many  echinoderms,  worms,  mollusks,  and  even  the  frog)  may  be 
artificially  stimulated  to  development  without  uniting  at  all  with  a 
spermatozoon.  The  resulting  individual  is  normal  in  every  respect 
except  that  instead  of  the  usual  diploid  number  it  has  only  the  single 
or  haploid  number  of  chromosomes.  Its  inheritance  of  course  is 
wholly  of  maternal  origin.  The  converse  experiment  in  echinoderms 
in  which  a  nucleus  of  male  origin  (that  is,  a  spermatozoon)  has  been 
introduced  into  an  egg  from  which  the  original  nucleus  has  been 
removed  shows  that  the  single  set  of  chromosomes  carried  by  the  male 
gamete  is  also  sufficient  to  cooperate  with  the  egg-cytoplasm  in 
developing  a  complete  individual. 

The  duality  of  the  body  and  the  singleness  of  the  germ. — Since 
every  maternal  chromosome  in  the  ordinary  cell  has  an  equivalent 
mate  derived  from  the  male  parent,  it  follows  therefore,  supposing  the 
chromosomes  do  have  the  significance  in  inheritance  attributed  to 
them,  that  as  regards  the  measurable  inheritable  differences  between 
two  individuals,  the  ordinary  organism  produced  through  the  union 


304     REx\DINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

of  the  two  germ-cells  is,  potentially  at  least,  dual  in  nature.  On  the 
other  hand  through  the  process  of  reduction  the  gametes  are  provided 
with  only  a  single  set  of  such  representatives.  This  duality  of  the 
body  and  singleness  of  the  mature  germ  is  one  of  the  most  striking  facts 
that  come  to  light  in  embryology.  How  well  the  facts  lit  in  with  the 
behavior  of  certain  hereditary  characters  will  be  seen  later  in  our  dis- 
cussions of  Mendelism. 

The  cytoplasm  not  negligible  in  inheritance. — Just  what  part  is 
played  by  the  cytoplasm  in  inheritance  is  not  clear,  but  it  is  probably 
by  no  means  a  negligible  one.  The  cytoplasm  of  a  given  organism 
is  just  as  distinctive  of  the  species  or  of  the  individual  of  which  it 
forms  a  part  as  are  the  chromosomes.  It  is  well  established  that 
neither  nucleus  nor  cytoplasm  can  fully  function  or  even  exist  long 
without  the  other,  and  neither  can  alone  produce  the  other.  They 
undoubtedly  must  cooperate  in  building  up  the  new  individual,  and 
the  cytoplasm  of  the  new  individual  is  predominantly  of  maternal 
origin.  It  is  obvious  that  all  of  the  more  fundamental  characters 
which  make  up  an  organism,  such,  for  instance,  as  make  it  an  animal 
of  a  certain  order  or  family,  as  a  human  being  or  a  dog  or  a  horse,  are 
common  to  both  parents,  and  there  is  no  way  of  measuring  how  much 
of  this  fundamental  constitution  comes  from  either  parent,  since  only 
closely  related  forms  will  interbreed.  In  some  forms,  moreover,  the 
broader  fundamental  features  of  embryogeny  are  already  established 
before  the  entrance  of  the  spermatozoon.  It  is  probable  therefore 
that  instead  of  asserting  that  the  entire  quota  of  characters  which  go 
to  make  up  a  complete  individual  are  inherited  from  each  parent 
equally,  we  are  justified  only  in  maintaining  that  this  equality  is 
restricted  to  those  measurable  differences  which  veneer  or  top  off,  as 
it  were,  the  individual.  We  may  infer  that  in  the  development  of  the 
new  being  the  chromosomes  of  the  egg  together  with  those  derived 
from  the  male  work  jointly  on  or  with  the  other  germinal  contents 
which  are  mostly  cytoplasmic  materials  of  maternal  origin. 

The  chromosomes  possibly  responsible  for  the  distinctiveness 
of  given  characters. — It  seems  probable  that  in  the  establishment  of 
certain  basic  features  of  the  organism  the  cooperation  of  the  cytoplasm 
with  chromatin  of  either  maternal  or  paternal  origin  might  accomplish 
the  same  end,  but  that  certain  distinctive  touches  are  added  or  come 
cumulatively  into  expression  through  influences  carried,  predomi- 
nantly at  least,  in  the  chromatin  from  one  as  against  the  other  parent. 
These  last  distinctive  characters  of  the  plant  or  animal  constitute  the 


THE  BEARERS  OF  THE  HERITAGE  305 

individual  differences  of  such  organisms.  In  this  connection  it  is  a 
significant  fact  that  in  young  hybrids  between  two  distinct  species  the 
early  stages  of  development,  especially  as  regards  symmetry  and 
regional  specifications,  are  exclusively  or  predominantly  maternal  in 
character,  but  the  male  influence  becomes  more  and  more  apparent  as 
development  progresses  until  the  final  degree  of  intermcdiacy  is 
attained. 

From  the  evidence  at  hand  this  much  seems  sure,  that  the  paternal 
and  maternal  chromosomes  respectively  carry  substances,  l)e  they 
ferments,  nutritive  materials  or  what  not,  that  are  instrumental  in 
giving  the  final  parity  of  personal  characters  which  we  observe  to  be 
equally  heritable  from  either  line  of  ancestry.  It  is  clear  that  most 
of  the  characters  of  an  adult  organism  cannot  be  merely  the  outcome 
of  any  unitary  substance  of  the  germ.  Each  is  the  product  of  many 
cooperating  factors  and  for  the  final  outcome  any  one  cooperant  is 
probably  just  as  important  in  its  way  as  any  other.  The  individual 
characters  which  we  juggle  to  and  fro  in  our  breeding  experiments  seem 
apexed,  as  it  were,  on  more  fundamental  features  of  organic  chemical 
constitution,  polarity,  regional  differentiation,  and  physiological 
balance,  but  since  such  individual  characters  parallel  so  closely  the 
visible  segregations  and  associations  which  go  on  among  the  chromo- 
somes of  the  germ-cells  it  would  seem  that  they,  at  least,  are  repre- 
sented in  the  chromosomes  by  distinctive  cooperants  which  give  the 
final  touch  of  specificity  to  those  hereditary  characters  which  can  be 
shifted  about  as  units  of  inheritance. 

Sex  and  heredity. — Whatever  the  origin  of  fertilization  may  have 
been  in  the  world  of  life,  or  whatever  its  earliest  significance,  the 
important  fact  remains  that  to-day  it  is  unquestionably  of  very  great 
significance  in  relation  to  the  phenomena  of  heredity.  For  in  all 
higher  animals,  at  least,  offspring  may  possess  some  of  the  character- 
istics originally  present  in  either  of  two  lines  of  ancestry,  and  this 
commingling  of  such  possessions  is  possible  only  through  sexual  repro- 
duction. As  has  already  been  seen,  in  the  pairing  of  chromosomes 
previous  to  reduction,  the  corresponding  members  of  a  pair  always 
come  together  so  that  in  the  final  segregation  each  gamete  is  sure  to 
have  one  of  each  kind  although  whether  a  given  chromosome  of  the 
haploid  set  is  of  maternal  or  paternal  origin  seems  to  be  merely  a 
matter  of  chance.  Thus,  for  instance,  if  we  arbitrarily  represent  the 
chromosomes  of  a  given  individual  by  ABC,  abc,  and  regard  A,B  and 
C  as  of  paternal  and  a,  h,  and  c  as  of  maternal  origin,  then  in  synapsis 


3o6      READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

only  yl  and  a  can  pair  together,  B  and  b^  and  C  and  c,  but  each  pair 
operates  independently  of  the  other  so  that  in  the  ensuing  reduction 
division  either  member  of  a  pair  may  get  into  a  cell  with  either  member 
of  the  other  pairs.  That  is,  the  line  up  for  division  at  a  given  reduc- 
tion might  be  any  one  of  the  following, 

7  ^     T.^     T>  •     This  would  yield  the  folio  wins;  eight  kinds  of 
aoc    aoC  aBC  aBc 

gametes,  ABC,  abc,  ABc,  abC,  Abe,  aBC,  AbC,  aBc,  each  bearing  one 
of  each  kind  of  chromosome  required  to  cover  the  entire  field  of 
characters  necessary  to  a  complete  organism.  And  since  each  sex 
would  be  equally  likely  to  have  these  eight  types  of  gametes  and  any 
one  of  the  eight  in  one  individual  might  meet  any  one  of  the  eight  of 
the  other,  the  possible  number  of  combinations  in  the  production  of  a 
new  individual  from  such  germ-cells  would  be  8X8,  or  64.  With 
the  larger  numbers  of  chromosomes  which  exist  in  most  animals  it  is 
readily  seen  that  the  number  of  possible  combinations  becomes  very 
great.  Thus  any  individual  of  a  species  with  twenty  chromosomes 
— and  many  animals,  including  man,  have  more — would  have  ten 
pairs  at  the  reduction  period  and  could  therefore  form  (2)^°,  or  1,024 
different  gametes  in  each  sex.  And  since  any  one  of  these  in  one 
sex  would  have  an  equal  chance  of  meeting  with  any  one  in  the  oppo- 
site sex,  the  total  number  of  possible  different  zygotes  that  might  be 
produced  would  be  (1,024)^,  or  1,048,576.  Sex,  therefore,  through 
recombinations  of  ancestral  materials,  undoubtedly  means,  among 
other  things,  the  production  of  great  diversity  in  offspring. 


CHAPTER  XXII 
VARIATION^ 

ERNEST  BROWN  BABCOCK  AND  ROY  ELWOOD  CLAUSEN 

Organic  differences,  their  nature  and  causes,  have  furnished 
abundant  material  for  speculative  enquiry  since  time  immemorial. 
The  great  significance  of  the  fact  of  organic  individuality  was  not  fully 
grasped  until  Lamarck  founded  his  theory  of  evolution  which  postu- 
lated the  progressive,  imperceptible  change  of  one  species  into  another. 
It  remained  for  Darwin  to  scrutinize  all  phases  of  organic  life,  past 
and  present,  wild  and  domesticated,  in  his  search  for  a  guiding  ])rin- 
ciple  which  should  explain  the  course  of  evolution.  Darwin's  hypothe- 
sis of  natural  selection  assumes  variability  without  enquiring  into 
its  causes,  but  this  does  not  mean  that  Darwin  was  not  concerned 
with  the  problem  of  causes.  In  both  his  Origin  of  Species  and 
Variation  in  Animals  and  Plants  under  Domestication  the  causes  of 
variability  are  often  referred  to  and  he  suggested  among  others,  the 
kind  and  amount  of  food,  climatic  changes  and  hybridization.  Our 
respect  for  the  great  naturalist's  keen  perception  deepens  when  we 
realize  that  very  little  has  been  added  as  yet  to  our  knowledge  of  the 
causes  of  variation. 

The  universality  of  variation. — Individuality  is  common  to  all 
organisms.  No  two  trees,  no  two  leaves,  no  two  cells  in  a  leaf  are 
identical  in  every  respect.  Individuals  sometimes  appear  exactly 
alike  but  even  identical  twins  will  be  found  to  differ  in  some  features. 
The  shepherd  knows  his  sheep  individually  and  the  orchardist  his  trees. 
Were  there  no  differences  in  individuals  there  would  be  no  changes  in 
species  and  there  could  be  no  improvement  of  cultivated  plants. 
''Variation  is  at  once  the  hope  and  despair  of  the  breeder,"  ib.c  hope 
because  without  it  no  improvement  would  be  possible,  the  desixiir 
because  very  often,  when  improvement  has  been  made,  variation 
results  in  a  tendency  to  fall  below  the  standard  previously  reached. 
In  the  sugar  beet,  for  example,  a  high  percentage  of  sugar  has  been 
maintained  by  continually  testing  and  selecting  the  ''mother"  beets 
for  the  next  crop  of  seed.     However,  this  necessity  for  continual 

^  From  E.  R.  Babcock  and  R.  E.  Clausen,  Genetics  in  Rehition  to  Ai^rieuHurr 
(copyright  1918).  Used  by  special  permission  of  the  publishers,  The  McClraw- 
Hill  Book  Company. 

307 


3o8      READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

selection  does  not  exist  in  respect  to  all  important  field  crops  although 
they  are  subject  to  the  general  law  of  variation.  That  this  must  be 
so  is  clear  when  we  realize  that  many  natural  species  as  well  as  culti- 
vated varieties  of  plants  are  really  mixtures  of  sub-species,  varieties,  or 
races  and  that  upon  being  isolated  these  distinct  forms  reproduce 
their  own  particular  type.  This  is  most  easily  demonstrated  in  plants 
normally  self-fertilized,  yet  in  all  naturally  cross-fertilized  plants  and 
in  higher  animals  this  same  endless  diversity  among  individuals  is 
even  more  marked. 

The  variation  concept. — As  we  have  implied  in  the  above  remarks 
the  term  variation  may  be  used  in  very  different  senses  in  referring 
to  different  phenomena.  Thus  variation  within  a  species  or  va'riety 
means  that  the  group  in  question  is  heterogeneous.  Among  indi- 
viduals variation  may  consist  of  differences  between  members  of  the 
same  generation  or  between  parents  and  offspring.  Even  when  thus 
restricted,  however,  the  term  is  apt  to  prove  ambiguous.  Hence  it  is 
necessary  to  give  some  thought  to  the  sources,  nature  and  causes  of 
these  individual  differences  in  order  that  we  may  use  clear-cut  expres- 
sions which  shall  always  convey  to  one  another  a  concept  of  the  same 
particular  sort  of  organic  difference. 

Classification  of  variations. — i.  Heritahility.  Character  differ- 
ences either  represent  something  specific  in  the  germ  or  they  are 
merely  the  effect  of  external  stimuli  upon  the  individual  soma.  In 
the  first  case  they  are  inherited,  although  they  will  not  reappear 
necessarily  in  all  later  generations  or  in  all  the  progeny.  In  the 
second  case  they  will  not  be  inherited.  This  is  a  fundamental  dis- 
tinction and  may  well  serve  as  our  primary  basis  of  classification. 
According  to  heritahility  variations  are  either  germinal  or  somatic. 
Under  germinal  variations  we  recognize  two  sub-classes,  combinations 
and  mutations.  Purely  somatic  variations  will  be  referred  to  here- 
after as  modifications. 

Modifications  are  non-heritable  differences  between  the  individuals 
of  a  race  caused  by  the  unequal  influence  of  different  environmental 
factors.  Such  variations  frequently  approximate  continuity  and, 
when  studied  statistically,  display  the  normal  variabiHty  curve, 
which  will  be  explained  in  a  subsequent  chapter.     [See  chap,  xxv.] 

Combinations  are  heritable  differences  between  the  individuals  of 
a  race  or  between  the  offspring  of  a  pair  of  parents  caused  by  segrega- 
tion and  recombination  of  hereditary  units.  They  also  frequently 
display  the  normal  variability  curve. 


VARIATION 


309 


Mutations  are  herital^le  differences  between  parents  and  offspring 
which  do  not  depend  upon  segregation  and  recombination. 

These  three  categories,  as  Baur  has  shown,  are  not  to  be  recognized 
and  separated  merely  according  to  appearances.  The  cause  of  any 
individual  differences  can  usually  be  established  only  by  careful 
breeding  experiments;  but  by  this  means  the  separation  of  the  three 
categories  is  always  possible  as  the  boundaries  between  them  are  quite 
sharp.  Modifications  are  somatic  effects  of  environmental  differences 
and  should  not  be  confused  with  germinal  changes  which  are  some- 
times induced  by  natural  or  artificial  means  and  which  result  in  the 
production  of  mutations.  Within  this  first  category  must  be  included 
all  place-effects  in  plants  and  somatic  environmental  effects  in  ani- 
mals. Modifications  comprise  a  large  portion  of  what  are  commonly 
spoken  of  as  fluctuations  due  to  environment,  but  all  cases  of  fluctua- 
ting variation  are  not  modifications  inasmuch  as  variations  due  to 
combinations  frequently  display  the  normal  variability  curve  also. 
Modifications  are  not  heritable.  The  second  category,  variation  by 
combination  of  hereditary  units  is  often  confused  with  modification, 
as  already  stated,  because  of  the  fact  that  variations  caused  by 
segregation  and  recombination  when  studied  statistically  often  dis- 
play the  normal  variability  curve.  This  is  especially  apt  to  be  the 
case  in  quantitative  characters  (those  of  size  or  weight)  and  segrega- 
tion and  recombination  may  be  the  cause  of  gradation  in  color  inten- 
sity. In  autogamous  (self-fertilized)  organisms  hybridization  between 
races  is  sufficiently  rare  to  be  negligible  in  this  connection,  i.  e.,  in  such 
species  the  fluctuating  variations  are  caused  by  the  environment. 
But  in  allogamous  organisms  (those  in  which  two  individuals  are 
necessary  to  accomplish  sexual  reproduction)  fluctuating  variations 
may  be  caused  either  by  the  environment,  by  segregation  and 
recombination  of  factors,  or  by  both  causes  acting  together.  We 
shall  take  up  the  third  category,  mutations,  in  a  later  chapter.  For 
the  present  it  is  sufficient  to  remember  that  mutations  are  no  doubt 
the  least  frequent  of  the  three  classes,  that  easily  distinguishable 
mutations  are  comparatively  rare,  but  that  there  may  also  occur  true 
mutations  of  such  moderate  extent,  as  compared  with  the  population, 
that  their  existence  would  only  be  detected  by  breeding  tests,  since 
their  progeny  would  exhibit  a  different  range  of  fluctuation  from  that 
of  the  population. 

2.  Nature.  We  may  next  enquire  into  the  nature  of  variation  as 
it  affects  the  organism.     Upon  this  basis  we  may  distinguish  between 


3IO     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

four   classes:    morphological,  physiological,  psychological  and  eco- 
logical. 

Morphological  variations  are  differences  in  size  and  form.  In 
general  morphological  variations  have  more  significance  for  the 
biologist  than  for  the  agriculturist.  However,  in  many  products  of 
the  farm,  size  and  conformation  are  of  decided  importance.  Two 
sub-classes  under  morphological  variations  are  meristic  and  homeotic 
variations.  Meristic  variations  are  diif  erences  in  number  of  repeated 
parts  such  as  the  petals  in  a  flower,  the  leaflets  in  a  compound  leaf  or 
number  of  phalanges.  Homeotic  variations  are  differences  caused  by 
the  replacement  of  one  part  by  another,  as  the  production  of  an 
antenna  in  place  of  an  eye  in  an  insect. 

Physiological  variations  are  differences  in  quality  and  performance. 
Examples  of  qualitative  variations  are  difference  in  degree  of  hardness 
of  bone,  flavor  of  meat,  richness  of  milk,  difference  in  normal  color, 
resistance  to  drouth,  frost  or  alkali.  Variations  in  performance  con- 
stitute the  most  important  group  for  the  producer.  Differences  in 
performance  are  sometimes,  though  not  necessarily,  associated  with 
certain  details  of  structure. 

Psychological  variations  are  differences  in  mental  traits.  That 
mental  and  nervous  conditions  have  very  definite  effects  upon  physical 
conditions  is  well  known,  but  the  problem  of  distinguishing  between 
purposeful  action  and  automatic  response,  between  manifestations  of 
reason  and  manifestations  of  instinct,  is  set  for  the  students  of  animal 
behavior.  While  variations  in  mental  characteristics  have  an  impor- 
tant place  in  eugenics  and  merit  the  attention  of  livestock  breeders, 
yet  the  inheritance  of  psychological  characters  must  be  more  exten- 
sively investigated  before  the  subject  can  be  considered  with  profit  in 
a  fundamental  study  of  genetics. 

Ecological  variations  are  those  differences  between  individuals  that 
result  from  their  fixed  relation  to  the  environment.  These  differences 
are  especially  noticeable  in  plants  and  are  known  as  place-effects  or 
place  variations.  This  category  includes  some  of  the  phenomena  of 
variation  in  crop  yield  and  hence  is  of  immediate  significance  to 
agriculture. 

3.  According  to  differences  between  them  there  are  two  general 
classes  of  variations:  first,  the  slight  differences  in  every  character 
which  are  always  to  be  observed  even  among  individuals  of  identical 
heredity;  second,  unusual,  striking  differences  commonly  known  as 
sports.     The  first  class  are  called  normal,  indefinite  fluctuating  or 


VARIATION  311 

continuous  variations  and  the  second,  abnormal,  definite  and  discon- 
tinuous variations.  It  should  be  noted,  however,  that  all  discontin- 
uous variations  are  not  necessarily  definite  or  even  distinguishable. 
Continuous  variations  when  examined  statistically  are  found  to  con- 
form to  the  law  of  statistical  regularity.  That  is,  if  measured  and 
plotted  the  graph  will  approximate  the  normal  curve  of  variability. 
Continuous  variations  are  either  heritable  (combinations)  or  non- 
heritable  (modifications)  and,  as  was  stated  above,  the  only  certain 
method  of  determining  the  class  in  which  "a  given  case  may  fall  is  the 
breeding  test.  Discontinuous  variations  are  essentially  discrete  dif- 
ferences whether  they  be  large  or  small.  They  are  also  either  herit- 
able and  there  is  no  correlation  between  size  and  heritability.  Thus 
the  extremely  large  and  small  mustard  plants,  considered  by  them- 
selves, are  discontinuous  variations,  but  they  are  almost  certainly  due 
entirely  to  environmental  difi'erences  and  seed  fr  m  the  small  plant  if 
grown  under  optimum  conditions  would  produce  plants  of  normal 
size.  On  the  other  hand,  it  is  known  that  many  minute  differences 
in  organisms  are  heritable. 

4.  According  to  direction  variations  are  classed  as  orthogenetic 
and  fortuitous.  Orthogenetic  variations  are  those  differences  found  in 
individuals  related  by  descent  which  form  progressive  series  tending 
in  a  definite  direction.  Many  remarkable  illustrations  are  found 
among  paleontological  records  of  the  evolution  of  animals.  Occa- 
sional examples  are  found  arnong  short-lived  or  vegetatively  propa- 
gated species.  The  remarkable  series  of  variations  of  the  Boston 
fern  is  a  good  example.  Fortuitous  variations  are  chance  ditTerences 
occurring  in  all  directions. 

5.  According  to  cause  variations  are  either  ectogcnctic,  differences 
arising  from  conditions  acting  upon  the  organism  from  without;  or 
autogenetic,  differences  resulting  from  strictly  internal  relations  be- 
tween germ  and  s^ma. 

Variation  and  development. — Somatogenesis,  in  sexually  produced 
multicellular  organisms,  includes  the  entire  history  o'  cellular  mulli- 
phcation  and  speciaHzation  from  the  first  cleavage  of  the  fertilized 
(or  parthenogenetic)  egg  to  the  completion  of  all  adult  features. 
From  the  standpoint  of  individual  development  it  includes  gamcto- 
genesis,  for  the  production  of  sexual  glands  and  of  secondary  sexual 
characters  are  merely  phases  of  differentiation.  Cell  growth  and  cell 
function  depend  directly  upon  the  activity  of  the  living  substance 
within  the  cell.     The  nature  and  degree  of  this  activity  depends  upon 


312      READINGS  IX  EVOLUTION,  GENETICS,  AND  EUGENICS 

two  sets  of  determining  causes  acting  simultaneously.  First,  there 
are  the  specific  hereditary  determiners  cr  genetic  factors,  which  react 
with  the  other  elements  of  the  protoplasm  and,  under  favorable 
circumstances,  condition  normal  development.  Second,  there  are  all 
the  conditions  external  to  the  cell  which  stimulate  or  inhibit  proto- 
plasmic activity.  These  "developmental  stimuli"  are  chemical  and 
physical  changes  wrought  by  energy  from  without  the  organism  or 
caused  by  its  own  physiological  activities.  Chemical  stimuli  are 
exerted  mainly  through  the"  medium  of  the  circulating  liquid  which 
surrounds  each  living  cell.  Normally  this  fluid  contains  the  elements 
essential  for  maintenance  of  life  as  well  as  various  waste  products. 
It  may  also  bear  toxic  substances  that  suppress  or  inhibit  the  cell 
functions  and  in  higher  animals  it  contains  the  secretions  of  the  duct- 
less, sexual  and  other  glands  that  profound^  affect  development. 
Physical  stimuli  are  exerted  chiefly  from  without  and  upon  the  organ- 
ism as  a  whole.  They  include  changes  in  temperature,  light  and 
density  of  medium,  the  effects  of  electric  and  radiant  energy,  force  of 
gravity,  etc.  Obviously,  so  many  interrelated  causes  acting  simulta- 
neously, each  being  independently  capable  of  inducing  a  change  in  the 
end  product,  may  cause  an  infinite  number  of  differences  in  substance 
and  in  degree  of  development. 

Variation  and  environment. — External  stimuli  affect  the  develop- 
ment of  characters  in  three  ways:  (i)  they  modify  the  development 
of  inherited  characters;  (2)  they  actually  condition  the  production  of 
characters  whose  hereditary  determiners  are  present  in  the  germ- 
plasm;  (3)  they  may  cause  germinal  variations  which  result  in  the 
appearance  of  new  heritable  characters.  The  following  are  illustra- 
tions of  these  effects  with  reference  to  particular  environmental 
factors. 

I.  Environment  modifies  development  of  inherited  characters. — 
{a)  Light  and  Function.  Klebs  reports  the  result  of  growing  the 
Showy  Sedum  {Sedum  spectahile)  in  white,  red,  and  blue  light.  The 
diverse  effects  of  the  three  kinds  of  light  are  clearly  shown  in  Fig.  5 1 . 
Although  the  visible  differences  between  the  three  plants  were  very 
pronounced  the  experiment  was  carried  much  farther.  During  1905--6 
observations  were  made  on  the  numbers  of  stamens  in  the  flowers 
of  plants  similarly  propagated  under  white,  red,  and  blue  light  and 
under  variations,  conditions  of  temperature,  moisture,,  and  food. 
About  20,000  flowers  were  examined  and  six  distinct  types  were  found, 
according  to  the  variation  in  number  of  stamens.     These  had  the 


VARIATIOX 


3^,i 


following  average  numbers  of  stamens:  (i)  9.68,  (2)  8.45,  f.^)  6.54, 
(4)  5-05.  (5)  947,  C6)  7.33.  Finally,  Klebs  subjected  similar  plants 
from  white,  red,  and  blue  light  to  chemical  analysis  in  order  to  secure 
further  evidence  of  the  physiological  effects  of  light  of  different  wave 


Fig.  51. — Sediini  spedahile.  The  three  shoots  (taken  from  a  sinfile  plant) 
were  planted  in  small  pots  on  March  12,  1904,  and  placed  in  different  greenhouses, 
/,  in  blue  light;  //,  in  mixed  white  light;  ///,  in  red  light.  Photographed  on 
September  30,  19 14.     {From  Bahcock  and  Clausen,  after  Klebs.) 


lengths.  Table  I  shows  the  composition  of  the  leaves  in  three  plants 
like  those  shown  in  Fig.  51.  They  were  in  their  respective  greenhouses 
from  June  6  to  September  7.  The  percentages  shown  are  per  100  g. 
of  dry  substance. 

In  comparing  these  percentages  it  should  be  remembered  thai  the 
plant  in  white  light  produced  1324  flower  buds  and  the  plant  in  red 
light  405,  while  the  plant  in  blue  light  produced  none.  This  explains 
the  higher  percentage  of  ash,  nitrogen  and  protein  in  the  last.  On 
the  other  hand,  the  amounts  of  starch  and  sugar  found  in  the  jdant 
from  white  Hght  are  decidedlv  larp^er  than  the  one  from  blue  light. 


314     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 


In  shortj  according  to  Klebs,  in  comparison  with  normal  white  light, 
the  production  of  organic  substances,  such  as  starch  and  sugar,  is 

TABLE  I 

Chemical  Composition  of  Three  Plants  of  Sedum  Spectahile  Grown  in 

White,  Red,  and  Blue  Light 


Substance 

Ash 

Sugar 

Calcium  malate 

Free  nitrogen 

Starch 

Crude  protein 


White 


13.20 

II  .04 

22 .  29 

o.  16 

5.82 

5-33 


Red 

13.  20 

15-40 
18  .02 

0-33 
3.66 

6.15 


Blue 


18.60 

2.40 

18.10 

0-59 
1 .  20 

7.64 


diminished  under  the  influence  of  blue  light  as  microchemical  and 
macrochemical  tests  distinctly  show.  In  consequence  of  this  dimin- 
ished assimilation   of  carbon  dioxide   the  rosettes   become  purely 


Fig.  52. — Above  the  diurnal  peacock  butterfly  {Vanessa  io),  and  below,  forms 
produced  by  subjecting  the  pupae  to  unusual  temperatures.  {From  Bahcock  and 
Clausen,  after  Goldschmidt.) 

vegetative.  In  red  light  the  carbon  assimilation  is  greater  than  in 
blue  light  but  less  than  in  white.  These  experiments  prove  that  the 
transformation  of  a  plant  "ripe  to  flower"  into  a  vegetative  one 


VARIATION 


315 


is  possible  on  the  one  hand  by  an  increase  of  temperature  and  of 
inorganic  salts,  and  on  the  other  hand  by  a  decrease  of  carbon 
assimilation. 

b)  Temperature  and  pigmentation.  Many  experiments  in  the 
rearing  of  moths  and  butterflies  under  controlled  temperatures  prove 
that  degree  of  pigmentation  is  profoundly  influenced  l)y  the  tem{)cra- 
ture  at  which  the  pupae  are  kept.  Some  species  exhibit  seasonal 
dimorphism  in  the  wild  state.  By  taking  pupae  of  the  common 
European  form  of  the  swallowtail  butterfly,  Papilio  machaon,  and 
subjecting  them  to  a  temperature  of  37°  to  38°  C,  Standfuss  obtainerl 
the  characteristic  summer  form  which  occurs  in  Palestine.  Again  it 
has  been  shown  by  temperature  experiments  that  many  variations 


28-VI 


30-VII 


15-IX 


Fig.  53. — Morphological   cycle   of   head   height   in  Hyalodaphnia.     Roman 
numerals  designate  months.     {From  Babcock  and  Clausen,  after  Woltcreck.) 

found  among  insects  in  nature  are  merely  aberrations  due  to  tempera- 
ture effects.  Goldschmidt  by  artificially  controlled  temperatures  has 
produced  a  series  of  forms  of  the  diurnal  peacock  butterfly,  Vanessa  io, 
which  show  the  fading  out  of  the  "peacock  eye"  mark  (see  Fig.  52). 
c)  Food  and  structure.  Woltereck  was  able  to  prove  that  the  form 
(hence  the  structure)  of  the  fresh  water  crustacean,  Hyalodaphnia, 
varies  directly  with  the  food  supply.  These  minute  animals  produce 
many  generations  during  a  season  and  the  successive  generations  from 
the  same  water  exhibit  a  morphological  cycle,  the  earlier  and  later 
generations  having  shorter  heads  and  the  generations  produced  from 
midsummer  to  autumn  having  longer  ones.  Fig.  53  is  a  reproduction 
of  Woltereck's  diagram  of  the  morphological  cycle  in  Hyalodaphnia 
showing  variation  in  head  and  shell  length  as  found  on  successive 


3i6 


READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 


dates  from  June  3  to  January  3.  By  raising  these  animals  under 
constant  temperature  conditions  and  varying  the  strength  of  the 
nutrient  solution,  Woltereck  proved  that  the  relative  size  of  body 
parts  varied  with  the  food.  In  Fig.  54  the  percentages  of  head  height 
to  shell  in  length  are  plotted  as  abscissas  and  the  numbers  of  indi- 
viduals as  ordinates.  Animals  from  three  strengths  of  nutrient  media 
were  measured,  the  curves  of  those  from  the  weaker,  the  medium  and 
the  richer  media  being  shown  at  mi,  ma  and  m3  respectively. 

d)  Moisture  and  plumage  color.  Beebe  experimented  with  the 
pigeon,  Scardafella  inca.  This  species,  as  found  in  North  and  Central 
America,  is  very  constant  in  color  of  plumage,  but  in  the  moist  tropics 


50        55         CO        65         70  '       75         80 

m2 


85 


90        95 

ni3 


Fig.  54. — Schematic  curves  of  head  height  in  Hyalodaphnia  as  grown  in 
media  of  three  different  food  values.  {From  Bahcock  arid  Clausen,  after 
Woltereck.) 


the  following  darker  colored  forms  occur:  in  Honduras,  dialeucos;  in 
Venezuela,  ridgwayi;  in  Brazil,  hrazilieiisls;  and  these  differ  in  the 
amount  of  pigment  in  the  feathers.  By  subjecting  the  birds  of  the 
northern  type  to  an  especially  moist  atmosphere,  Beebe  caused  them 
to  be  so  influenced  that  with  each  new  moulting,  whether  natural  or 
artificially  induced,  they  always  developed  darker  feathers.  Thus  a 
wild  bird  having  pigment  in  25.9  per  cent  of  its  area,  would  have  after 
the  second  moulting  under  experimental  conditions,  38  per  cent  and 
after  the  third,  41.6  per  cent.  Thus  during  the  experiment  the 
typical  form  assumed  the  appearance  of  the  three  other  forms  and 
finally  developed  plumage  markings  which  have  never  been  seen  in 
nature.  Fig.  55  shows  the  type  form,  inca,  the  three  geographical 
variants,  and  the  darkest  artificially  produced  form. 


VARIATION' 


317 


2.  Environment  conditions  development  of  inherited  characters.— 
(a)  Light  and  metabolism.  In  a  general  sense  light  conditions  life 
in  all  normally  green  plants.  It  certainly  conditions  normal  develop- 
ment in  such  plants.  Potatoes  sprouted  in  a  dark  room  develop  no 
chlorophyll  in  the  stems  and  the  rudimentary  leaves  are  abortive. 
In  many  bulbous  plants,  however,  the  influence  of  moisture  and  heat 
are  sufficient  to  induce  leaf  growth  and  even  development  of  the 
iniiorescense,  but  it  is  all  done  at  the  expense  of  the  food  storcrl  up  in 
the  bulbs. 


Fig.  55. — a,  Typical  wild  pigeon,  Scardafclla  inca;  b,  the  form  dialcucos;  r, 
hraziliensis;  d,  ridgwayi;  e,  inca  after  three  moultings  in  a  moist  atmosphere. 
(After  Beebe,  from  Babcock  and  Clausen.) 


b)  Temperature  and  flower  color.  Baur  reports  an  experiment  with 
a  red  variety  of  the  Chinese  primrose,  Primula  sinensis  rubra.  If 
plants  of  this  variety  are  raised  by  the  usual  method  until  about  one 
week  before  time  to  bloom  and  then  some  of  the  plants  are  put  in  a 
warm  room  under  partial  shade  (temperature  from  ^0°  to  35°  C.)  and 
the  remainder  in  a  cool  house  (temperature  from  15°  to  20°  C),  when 
they  bloom  those  in  the  warm  temperature  have  pure  white  flowers 
while  those  in  the  cool  temperature  have  the  normal  red  color  of  the 
variety.     Moreover,  if  plants  are  brought  from  the  warm  into  the 


3i8      READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

cool  temperature  the  flowers  which  develop  later  on  will  be  normal 
red  in  color.  Thus  it  cannot  be  said  that  this  primula  inherits  either 
red  or  white  flowers.  WTiat  it  really  inherits  is  ability  to  react  in 
certain  ways  under  the  influence  of  temperature. 

c)  Food  and  fertility.  It  is  well  known  that  the  kind  of  food 
supplied  to  the  larvae  of  bees  determines  whether  the  females  shall  be 
fertile  (queens)  or  infertile  (workers).  The  striking  differences  in 
structure  and  instincts  of  the  two  classes  of  females  are  all  conditioned 
by  the  food  provided  for  the  larvae.  Each  larva  inherited  the  capacity 
to  react  in  either  way  according  to  the  stimulus  received. 

d)  Moisture  and  structure.  Morgan  reports  a  variety  of  the 
pomace  fly,  Drosophila  ampelophila,  with  abnormal  abdomen;  "the 
normal  black  bands  of  the  abdomen  are  broken  and  irregular  or  even 
entirely  absent.  In  flies  reared  on  moist  food  the  abnormality  is 
extreme;  but  even  in  the  same  culture  the  flies  that  continue  to 
hatch  become  less  and  less  abnormal  as  the  culture  becomes  more 
dry  and  the  food  scarce,  until  finally  the  flies  that  emerge  later  cannot 
be  told  from  normal  flies.  If  the  culture  is  kept  well  fed  (and  moist) 
the  change  does  not  occur,  but  if  the  flies  are  reared  on  dry  food,  they 
are  normal  from  the  beginning." 

3.  Environment  may  cause  new  heritable  characters. — ^As  yet 
there  is  a  dearth  of  evidence  which  can  be  accepted  as  scientific  proof 
that  external  stimuli  actually  cause  germinal  variations.  At  the  same 
time  there  is  an  abundance  of  data  which  falls  into  the  class  of  circum- 
stantial evidence  in  favor  of  such  a  doctrine.  Moreover,  there  are 
a  few  cases  in  which  new  heritable  characters  have  been  artificially 
produced  by  carefully  controlled  external  stimuli.  Hence  some 
germinal  variations  are  apparently  caused  by  known  environmental 
conditions  and  we  are  justified  in  recognizing  this  third  category  of 
developmental  differences  due  to  environmental  effects. 

Considerable  evidence  of  permanent  changes  in  both  morphologi- 
cal and  physiological  characters  has  been  secured  from  experiments 
with  the  culture  of  bacteria  and  yeast,  in  unusual  culture  media,  in 
the  presence  of  toxic  solutions,  or  under  extreme  temperature  condi- 
tions. The  significant  results  of  four  investigators  who  worked 
independently,  Hansen,  Barber,  Wolf,  and  Jordan,  have  been  reviewed 
and  discussed  in  regard  to  their  bearing  on  genetic  theory  by  Cole 
and  Wright.  The  four  investigators  mentioned  above  used  refined 
methods  and  three  of  them  began  by  isolating  a  single  organism  from 
whose  progeny   they  obtained   distinct   strains  or  biotypes  which 


VARIATION  319 

remained  constant  for  hundreds  of  test-tube  "generations/'  Ii  must 
be  admitted  that  in  most  of  these  cases  no  specific  inlluences  can  be 
named  as  the  direct  cause  of  the  inherited  variation.  But  there  is  no 
longer  any  doubt  that  permanent,  discontinuous  variations  do  occur 
spontaneously  in  these  lowest  organisms,  and  it  is  highly  probable 
that  certain  incidental,  external  forces  play  an  important  part  in 
inducing  such  variations. 

Direct  experimental  attack  upon  the  germ  cells  themselves  has 
been  made  with  plants  by  a  number  of  investigators,  notably  bv 
MacDougal,  who  injected  very  dilute  solutions  of  potassium  iodide, 
zinc  sulphate,  sugar,  etc.,  directly  into  the  ovaries  of  various  plants 
immediately  before  fertilization.  Consequently  somatic  changes  have 
been  produced  which  were  inherited  throughout  several  generations. 


Fig.  56. — 0,  portion  of  leaf  of  Scrophularia  showing  branching  lateral  view; 
D,  branching  vein  replaced  by  two  laterals  in  leaf  of  seedling  grown  from  seed 
produced  by  an  injected  ovary.  Also  note  the  difference  in  size  and  margin  of 
leaves.     {From  Babcock  and  Clausen,  after  MacDougal.) 

By  means  of  check  experiments  and  observations  it  was  found  that 
these  germinal  variations  were  not  caused  by  the  wounding  of  the 
ovary  and  it  is  thought  that  they  must  have  been  induced  in  some  way 
by  the  presence  of  the  foreign  chemical  solution  in  the  ovary.  Fig.  56 
shows  a  morphological  change  which  appeared  in  a  seedling  of  an 
unnamed  species  of  Scrophularia  as  a  result  of  ovarial  injection.  Hav- 
ing tested  the  species  sufficiently  to  determine  that  it  was  a  simple  one, 
MacDougal  treated  several  ovaries  with  potassium  iodide,  one  part 
in  40,000  and  secured  seed.  No  other  species  of  Scrophularia  grew 
near  the  cultures.  From  this  seed  only  three  plants  were  raised. 
''One  formed  a  shoot  fairly  equivalent  to  the  normal,  finally  producing 
flowers  in  which  the  anthocyans  were  of  a  noticeal^ly  deep  hue.  The 
two  remaining  plantlets  were  characterized  by  a  succulent  aspect  of 
the  leaves  and  by  a  lighter  and  yellow  color  of  the  leaves  and  stems. 


320      READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

The  flowers  on  one  of  the  derivatives,  as  they  may  be  called,  were  so 
completely  lacking  in  color  as  to  be  a  cream-white,  this  derivative 
being  designated  as  alhida,  while  the  other  showed  some  marginal 

color  and  a  rusty  tinge  and  was  designated  as  rufida Seeds  of 

the  original  two  derivatives  were  sowed  in  the  greenhouse.  But  one 
plant  of  albida,  the  most  extreme  departure,  survived,  while  four  of 
rufida  were  secured."  MacDougal  compared  these  second  generation 
seedlings  with  seedlings  from  the  original  stock  of  the  species,  noting 
differences  in  size  and  margin  of  leaves,  length  of  petioles  and  number 
of  marginal  glands.  He  found  that  the  differences  shown  by  the  first 
generation  appeared  again  in  the  second  generation.  Striking  as  these 
results  appear  it  must  be  admitted  that  it  would  be  difficult,  on  account 
of  the  small  numbers  of  individuals  differing  from  the  parent  type,  to 
prove  satisfactorily  to  the  biometrician  that  they  were  not  mutations 
which  would  have  occurred  regardless  of  the  ovarial  treatment. 

What  appear  to  be  germinal  variations  in  the  tomato  have  been 
induced  by  intensive  feeding.  T.  H.  White  tested  the  effect  of  dried 
blood,  dissolved  phosphate  rock,  sulphate  of  potash  and  iron  filings 
all  in  excessive  amounts,  and  (with  the  exception  of  the  iron)  in 
various  combinations,  on  the  Red  Cherry  tomato.  The  lack  of  data 
on  control  cultures  of  seedlings  from  the  same  parent  as  the  experi- 
mental cultures  makes  it  impossible  to  compare  the  actual  amount 
of  permanent  variation  produced.  T.  H.  White  states  that  measure- 
ments "show  that  the  plants  of  the  sixth  generation  growTi  under  the 
influence  of  the  dried  blood  are  one-third  larger  in  height,  length  of 
leaf  and  size  of  fruit,  than  those  of  the  second."  The  author  con- 
cludes that  ''there  can  be  no  doubt  ....  that,  in  the  case  of  Red 
Cherry  treated  with  dried  blood,  there  is  permanent  variation  to  the 
third  generation."  If  these  results  are  corroborated  by  more  care- 
fully planned  and  rigidly  controlled  experiments  they  will  add  the 
weight  of  scientific  proof  of  a  principle  in  plant  breeding  long  since 
recognized  on  empirical  grounds,  to  wit,  that  the  introduction  of  wild 
plants  into  intensive  cultivation  induces  variation.  Furthermore,  it 
suggests  a  possible  means  for  rapid  permanent  improvement  of  wild 
forms  with  which  hybridization  may  be  impracticable. 

In  experiments  on  lower  animals,  e.g.,  the  protozoa,  the  same 
difficulty  is  met  with  as  has  been  encountered  in  bacteria  and  yeasts, 
in  that  it  is  manifestly  impossible  to  distinguish  between  somatic  and 
germinal  variations.  Moreover,  in  most  of  these  experiments,  as  with 
most  of  those  on  higher  animals,  the  necessary  conditions  for  rigid 


VARIATION 


321 


scientific  analysis  have  been  lacking.  Either  the  same  strain  as  was 
subjected  to  artificial  conditions  was  not  grown  for  comparison  under 
natural  conditions  or  else  the  conditions  themselves  were  not  suffi- 
ciently well  controlled  to  permit  of  certain  analysis.  It  is  interesting 
to  note  that  the  pomace  fly,  Drosophila  ampelophila,  which  has  pro- 
duced more  mutations  so  far  as  we  know  than  any  other  organism, 
was  subjected  to  the  effects  of  ether  on  a  grand  scale  and  under 
controlled  conditions  by  Morgan,  but  that  not  a  single  mutation  was 
observed  to  result  from  this  treatment.  However,  mutations  have 
subsequently  appeared  again  and  again  in  cultures  of '''wild"  flies  not 
only  of  this  species  but  also  of  other  species  of  Drosophila.  Thus  it 
appears  that  germinal  variations  frequently  occur  independently  of 
external  stimuli.  It  also  seems  that  a  tendency  to  produce  mutations 
may  be  inherited. 

With  animals  the  best  known  experiments  on  the  artificial  pro- 
duction of  germinal  variations  are  those  of  Tower  who  worked  with 
the  Colorado  potato  beetle,  Leptinotarsa  decemlineata,  and  related 
species.  Like  other  arthropods  these  beetles  are  more  directly  under 
the  influence  of  temperature  changes  at  least  than  are  warm-blooded 
animals.  Tower  first  determined  the  period  in  ontogeny  when  ex- 
ternal stimuli  will  affect  the  germ  cells.  He  found  that  in  Leptino- 
tarsa the  germ  cells  do  not  become  susceptible  to  external  stimuli 
until  after  the  time  in  ontogeny  when  the  color  pattern  of  the  individ- 
uals subjected  to  the  stimuli  can  be  influenced.  He  found  that  eggs 
were  most  susceptible  just  before  and  during  maturation  and  this 
observation  is  in  agreement  with  those  of  Fischer,  Standfuss,  Weis- 
mann  and  others  who  have  conducted  similar  investigations.  Tower 
concluded  that  certain  individuals  from  the  germ  cells  of  a  stimulated 
parent  ''show  intense  heritable  variations,  whereas  those  not  acted 
upon  do  not  show  these  changes."  Most  of  the  inherited  variations 
involve  changes  in  the  pigmentation  of  the  body  parts.  In  certain 
cases  there  was  an  actual  change  in  the  color  pattern.  It  is  to  these 
results  that  Tower  attaches  the  greatest  significance  inasmuch  as 
most  similar  experiments  have  not  succeeded  in  causing  pattern 
changes.  In  spite  of  the  elaborateness  of  Tower's  methods  consider- 
able skepticism  exists  regarding  the  validity  of  his  conclusions,  and 
this  has  not  been  lessened  by  the  non-appearance  of  confirmatory 
data.  In  a  recent  paper  he  reports  the  production  of  very  striking 
germinal  modifications  in  L.  decemlineata  as  a  result  of  subjecting  a 
morphologically  homogeneous  race  to  an  extreme  change  in  environ- 


322     READINGS  IN  EVOLUTION,  GENETICS,  AND   EUGENICS 

ment.  However,  it  is  still  a  question  whether  the  material  used  may 
not  be  heterogeneous  as  regards  the  germinal  factors  that  condition 
certain  physiological  characters. 

Stockard's  investigations  on  the  effect  of  alcohol  on  the  progeny 
of  guinea  pigs  have  shown  that  the  germ  cells  as  well  as  the  somatic 
tissues  of  the  alcoholized  animals  are  injured. 

On  the  whole  it  must  be  admitted  that  the  experimental  induction 
of  heritable  variations  is  still  largely  an  unworked  field.  The  complex 
conditions  to  be  considered  and  consequent  obstacles  to  be  overcome 
are  appreciated  by  no  one  more  fully  than  by  those  who  have  at- 
tempted such  investigations.  For,  as  Tower  has  said:  "It  is  evident 
that  the  problem  of  germinal  change  is  one  of  difficulty,  and  involves 
more  of  indirect  than  of  direct  methods  of  investigation.  There  is 
little  reason  to  expect  that  present  biochemical  methods  can  give  a 
solution,  but  they  may  give  valuable  suggestions  for  further  indirect 
investigation.  It  seems  not  improbable,  however,  that  this  problem, 
like  so  many  others  in  biology,  must  await  the  solution  of  the  larger 
question  of  what  life  is  before  it  will  be  possible  to  express  in  exact 
terms  the  nature  of  germinal  changes.  Our  present  status,  with 
several  methods  of  production  and  much  knowledge  of  the  behavior 
of  induced  germinal  changes  available,  is  a  basis  from  which  great 
advances  in  knowledge  and  in  operation  may  reasonably  be  expected." 


CHAPTER  XXIII 

ARE  ACQUIRED  CHARACTERS  (MODIFICATIONS) 

HEREDITARY  ? 

Introductory  Note. — In  the  previous  chapter,  under  the  heading  "Classifica- 
tion of  Variations,"  the  authors  pointed  out  that  germinal  variations  are  hereditary, 
and  somatic  variations  (modifications)  are  not  hereditary.  That  germinal  varia- 
tions are  hereditary  and  may  be  produced  in  a  number  of  different  ways  was  made 
clear  in  the  last  chapter,  but  the  statement  that  somatic  modifications  are  never 
in  the  least  hereditary  is  equivalent  to  a  total  denial  of  the  doctrine  of  the 
"Inheritance  of  Acquired  Characters,"  the  so-called  Lamarckian  theory',  which  was 
briefly  presented  in  chapter  ii. 

This  is  not  a  closed  question  and  the  final  answer  has  been  given  neither  in 
the  negative  nor  in  the  affirmative.  The  problem  is  of  utmost  import  for  evolu- 
tionists and  for  all  who  are  interested  in  race  improvement.  So  important  is  it 
to  view  this  question  fairly  that  we  shall  quote  extensively  from  several  of  the 
leading  students  of  the  problem. 

MISUNDERSTANDINGS   AS   TO   THE    QUESTION   AT   ISSUE^ 

J.    .\RTHUR   THOMSON 

The  precise  question  is  this:  Can  a  structural  change  in  the  body 
induced  by  some  change  in  use  or  disuse,  or  by  a  change  in  surrounding 
influence,  affect  the  germ-cells  in  such  a  specific  or  representative  way 
that  the  offspring  will  through  its  inheritance  exhibit,  even  in  a  slight 
degree,  the  modification  which  the  parent  acquired  ? 

Before  we  pass  to  discuss  the  evidence  pro  and  con  it  will  be  useful 
to  notice  some  frequently  recurring  misunderstandings,  the  persistence 
of  which  would  make  further  argument  futile. 

Misunderstanding  I. —  How  can  there  be  progressive  evolution  if 
acquired  characters  are  not  transmitted  ? — Those  who  have  not  thought 
clearly  on  the  subject  often  shake  their  heads  sagely  and  remark  that 
they  "do  not  see  how  evolution  could  have  been  possible  at  all  unless 
what  is  acquired  by  one  generation  is  handed  on  to  the  next."  To 
this  we  have  simply  to  answer  (i)  that  our  first  business  is  to  find  out 
the  facts  of  the  case,  careless  whether  it  makes  our  interpretation  of 
the  history  of  life  more  or  less  difhcult,  and  (2)  that  in  the  supply  of 
germinal  variations,  whose  transmissibility  is  unquestioned,  there  is 
ample  raw  material  for  evolution.  We  know  a  Httle  about  the  abundant 

'  From  J.  A.  Thomson,  Heredity  (copyright  1907).  Used  by  special  permis- 
sion of  the  publisher,  John  Murray,  London. 

323 


324      READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

crop  of  variations  at  present  supplied;  there  is  no  reason  to  believe 
that  it  was  less  abundant  in  the  past. 

Misunderstanding  II. — Interpretations  are  not  fads. — There  are 
many  adaptive  characters  in  plants  and  animals  which  may  be  super- 
ficially interpreted  as  due  to  the  direct  result  of  use  and  disuse  or 
of  environmental  influence.  The  Lamarckians  have  so  interpreted 
them,  and  the  Lamarckian  way  of  looking  at  adaptations  has  become 
habitual  to  many  uncritical  minds.  They  see  on  modern  flowers  the 
footprints  of  insects  which  have  visited  them  for  untold  ages;  they 
speak  of  the  dwindling  of  the  whale's  hind-limbs  through  disuse,  of  the 
hardening  of  the  ancestral  horses'  hoofs  as  they  left  the  marshes  and 
ran  oh  harder  ground;  they  picture  the  giraffe  by  persistent  effort 
lengthening  out  its  neck  a  few  millimetres  every  century,  as  the  acacia 
raised  its  leaves  higher  and  higher  off  the  ground;  and  they  say  that 
animate  nature  is  so  full  of  evidences  of  the  inheritance  of  acquired 
characters  that  no  further  argument  is  needed. 

But  all  this  is  a  begging  of  the  question.  It  is  easy  to  find  struc- 
tural features  which  may  he  interpreted  as  entailed  acquired  characters, 
if  acquired  characters  can  be  entailed.  Obviously,  however,  we  must 
deal  with  what  we  can  prove  to  be  modifications,  or  with  what  we  can 
plausibly  regard  as  modifications  because  we  find  their  analogues  in 
actual  process  of  being  effected  to-day. 

It  is  easy  to  say  that  the  blackness  of  the  negro's  skin  was  produced 
by  the  tropical  sun,  and  that  it  is  now  part  of  his  natural  inheritance. 
It  is  easy  to  say  this,  but  absolutely  futile.  Let  us  first  catch  our 
modifications. 

The  Golden  Rod  {Solidago  virgaurea)  growing  on  the  Alps  is  pre- 
cocious in  its  flowering  when  compared  with  representatives  of  the 
same  species  growing  in  the  lowlands.  Hoffmann  found  that  Alpine 
forms  transplanted  to  Giessen  remained  precocious,  therefore  the 
acquired  precocity  had  become  heritable.  But  there  is  no  evidence 
that  the  precocity  was  acquired;  it  may  have  been  the  outcome  of  the 
selection  of  germinal  variations. 

The  African  Wart-hog  {Phacochoerus)  has  the  peculiar  habit  of 
kneeling  down  on  its  fore-limbs  as  it  routs  with  its  huge  tusks  in  the 
ground  and  pushes  itself  forward  with  its  hind-limbs.  It  has  strong 
horny  callosities  protecting  the  surfaces  on  which  it  kneels,  and  these 
are  seen  even  in  the  embryos.  This  seems  to  some  naturalists  to  be  a 
satisfactory  proof  of  the  inheritance  of  an  acquired  character.  It  is  to 
others  simply  an  instance  of  an  adaptive  peculiarity  of  germinal  origin 
wrought  out  by  natural  selection. 


ARE  ACQUIRED  CHARACTI-RS  HKKKI)rr.\R\?  325 

Misunderstanding  Ill.—Begging  the  question  by  darting  with 
what  is  not  proved  to  be  a  modification. — There  is  no  relevancy  in  citing 
cases  where  an  abnormal  bodily  peculiarity  re-appears  generation 
after  generation,  unless  it  be  shown  that  the  peculiarity  is  a  modifica- 
tion, and  not  an  inborn  variation  whose  transmissibility  is  admitted 
by  all.  Short-sightedness  may  recur  in  a  family-series  generation 
after  generation,  but  there  is  no  evidence  to  prove  that  the  original 
short-sightedness  was  a  modification.  In  all  probability,  short- 
sightedness is  in  its  origin  a  germinal  variation,  like  so  many  other 
bodily  idiosyncrasies. 

In  regard  to  some  diseases,  such  as  rheumatism,  it  is  often  said 
dogmatically  by  those  who  know  little  about  the  matter  that  the 
original  affection  in  the  ancestor  was  brought  about  by  some  definite 
external  influence — such  as  a  cold  drive  or  a  damp  bed;  but  it  seems 
practically  certain  that  in  all  such  cases  we  have  to  do  with  an  inborn 
predisposition,  to  the  expression  of  which  the  cold  drive  or  the  damp 
bed  were  merely  the  liberating  stimulus,  comparable  to  the  pulling  of 
the  trigger  in  a  loaded  gun.  The  liberating  stimulus  is,  of  course,  of 
great  importance,  both  in  the  case  of  the  gun's  discharge  and  the 
organism's  disease,  but  it  only  goes  a  little  way  towards  a  satisfactory 
interpretation  in  either  case.  Not  that  we  can  explain  the  origin  of 
rheumatism  or  shortsightedness  or  any  such  thing — there  is  no  expla- 
nation in  calling  them  germinal  variations  that  cropped  up;  but  we 
are  almost  certain  that  they  never  are  modifications  or  acquired 
characters. 

Herbert  Spencer  twits  those  who  are  sceptical  as  to  the  trans- 
mission of  acquired  modifications  with  assigning  the  most  flimsy 
reasons  for  rejecting  a  conclusion  they  are  averse  to;  but  when  Spencer 
cites  the  prevalence  of  short-sightedness  among  the  ''notoriously 
studious"  Germans,  the  inheritance  of  a  musical  talent,  and  the  inheri- 
tance of  a  liabiHty  to  consumption,  as  evidence  of  the  inheritance  of 
modifications,  we  are  reminded  of  the  pot  calling  the  kettle  black. 

Over  and  over  again  in  the  prolific  literature  of  this  discussion  the 
syllogism  is  advanced,  either  in  regard  to  gout  or  something  analogous — 

Gout  is  a  modification  of  the  body,  an  acquired  character; 

Gout  is  transmissible; 

Modifications  are  sometimes  transmissible. 
It  may  be  formally  a  good  argument,  but   there  is  every  reason   to 
deny  the  major  premise.     There  is  no  proof  that  the  gouty  habit  had 
an  exogenous  origin — that  it  was,  to  begin  with,  for  instance,  the 
direct  result  of  high  living;    though  it  is    generally   admitted  that 


326     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

excesses  in  eating  or  drinking  may  give  a  stimulus  to  its  expression. 
''The  conclusion  that  I  have  arrived  at,"  says  Prof.  D.  J.  Hamilton, 
"is  that  the  gouty  habit  of  body  has  arisen  as  a  variation,  and  as  such 
is  hereditarily  transmissible,  and  that  excess  of  diet  and  alcohol  merely 
renders  the  habit  of  body  apparent."  It  may  also  be  pointed  out  that 
gout  and  rheumatism  and  the  like  are  rather  processes  of  metabolism 
than  structural  modifications,  though  the  latter  may  ensue. 

After  pointing  out  the  irrelevancy  of  citing  cases  of  the  hereditary 
recurrence  of  polydactylism,  haerriophilia,  colour-blindness  in  man, 
or  the  absence  of  horns  in  cattle  or  of  tails  in  cats,  as  instances  of  the 
transmission  of  acquired  characters.  Prof.  Ernst  Ziegler  says:  "Only 
that  can  be  regarded  as  '  acquired '  which  is  produced  in  the  course  of 
the  individual  life,  during  and  after  the  period  of  development,  exclu- 
sively under  the  influence  of  external  conditions;  the  term  is  in  no 
wise  applicable  to  peculiarities  which,  as  one  says,  arise  of  themselves 
from  a  predisposition  already  present  in  the  germ." 

Misunderstanding  IV. — Mistaking  the  reappearance  of  a  modifica- 
tion for  transmission  of  a  modification. — It  is  of  little  service  to  cite 
cases  where  a  particular  modification  reappears  generation  after  gen- 
eration unless  it  be  shown  that  the  change  recurs  as  part  of  the  inheri- 
tance, and  not  simply  because  the  external  conditions  which  evoked  it 
in  the  first  generation  still  persisted  to  evoke  it  in  those  that  followed. 
Reappearance  is  not  synonymous  with  inheritance. 

Misunderstanding  V. — Mistaking  re-infection  for  transmission. — 
A  particular  form  of  the  fourth  misunderstanding  has  to  do  with  facts 
so  special  that  it  may  be  conveniently  treated  of  separately.  It  has 
to  do  with  microbic  diseases.  It  is  admitted  that  a  parent  infected 
with  tubercle-bacillus  or  with  the  microbe  of  syphilis  may  have  off- 
spring also  infected.  But  such  cases  are  irrelevant  in  the  discussion. 
Infection,  whether  before  or  after  birth,  has  nothing  to  do  with  inheri- 
tance. As  Dr.  Ogilvie  says,  "Wherever  the  transmission  of  infectious 
disease  from  parent  to  offspring  has  been  adduced  to  support  the 
doctrine  of  the  inheritance  of  acquired  characters,  it  has  been  done  in 
utter  misconception  of  its  meaning  and  scope." 

Medical  men  have  sometimes  condescended  to  make  a  subtle 
distinction  between  "hereditary"  and  "congenital"  syphiHs — the 
latter  manifested  at  birth,  the  former  some  time  afterwards!  It  seems 
strange  that  they  have  failed  to  recognise  that  there  is  no  reason  to  use 
the  word  "hereditary"  at  all  in  this  connection.  What  occurs  is  an 
infection,  and  it  is  theoretically  immaterial  at  what  stage  the  infection 
occurs.    A  microbe  cannot  be  part  of  an  inheritance. 


ARE  ACQUIRED  CHARACTERS  IIEREDITARV? 


•y  f 


Misunderstanding  Yl.~Trausmission  in  unicellular s  is  not  to  the 
point.— It  is  not  to  the  point  to  cite  cases  where  unicellular  organisms, 
such  as  bacteria  or  monads,  have  been  profoundly  and  heritably  modi- 
lied  by  artificial  culture,  so  that,  for  instance,  the  descendants  of  a 
virulent  microbe  have  been  made  to  lose  their  evil  potency.  It  is 
irrelevant  because  in  regard  to  unicellular  organisms  we  cannot  draw 
the  distinction  between  body  and  germinal  matter,  apart  from  which 
the  concept  of  modifications  is  of  no  value.  In  artificial  culture  the 
whole  character  of  the  unicellular  organism — its  particular  metabolism 
— is  altered;  it  multiplies  by  dividing  into  two  or  more  parts,  which 
naturally  retain  the  altered  constitution.  But  this  is  worlds  away 
from  the  supposed  case  of  an  alteration  in  the  structure  of  the  little  toe 
so  affecting  the  germ-cells  that  the  offspring  inherit  a  corre.sponding 
deformation. 

Professor  L.  Errera  (1899)  reported  an  experiment  with  a  simi)le 
but  multicellular  mould  {Aspergillus  niger),  which  adapted  itself  to  a 
medium  more  concentrated  than  the  normal.  The  second  generation 
of  the  mould  was  more  adapted  than  the  first,  and  the  adaptation  to 
the  concentrated  medium  was  not  wholly  lost  after  rearing  in  the  nor- 
mal medium  again.  This  looks  like  evidence  of  the  inheritance  of  the 
acquired  adaptive  quality  which  was  brought  about  as  a  direct  modifi- 
cation. But  the  case  does  not  really  help  us,  since  the  distinction 
between  soma  and  germ-plasm  is  not  more  than  incipient  in  the  mould 
in  question.  And  even  if  the  distinction  were  more  marked,  it  would 
only  show  that  the  germ-plasm  is  capable  of  being  affected  along  with 
the  body,  by  a  deeply  saturating  influence,  which  nobody  has  ever 
denied. 

Misunderstanding  VII. — Changes  in  the  germ-cells  along  with 
changes  in  the  body  are  not  relevant. — Another  misunderstanding  is  due 
to  a  failure  to  appreciate  the  distinction  between  a  change  of  the  repro- 
ductive cells  along  with  the  body,  and  a  change  in  the  reproductive 
cells  conditioned  by  and  representative  of  a  particular  change  in 
bodily  structure.  The  supporters  of  the  hypothesis  that  modifications 
may  be  transmitted  point  to  the  tragic  cases  where  some  })oisoning  of 
the  parent's  system,  by  alcohol,  opium,  or  some  toxin,  is  followed  by 
some  deterioration  in  the  offspring.  There  is  no  doubt  as  to  the  fact; 
the  question  is  as  to  the  correct  interpretation. 

I.  In  some  cases  it  may  be  that  the  whole  system  of  the  jxirent  is 
poisoned— reproductive  cells  as  well  as  body;  the  effect  may  be  as 
direct  On  the  germ-cells  as  on  the  nerve-cells.  These,  therefore,  are  not 
cases  on  which  to  test  the  transmissibility  of  an  acquired  character— i.e., 


328     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

of  a  particular  somatic  modification.  If  a  local  poisoning  had  a 
structural  effect  on  some  particular  organ,  and  if  that  structural  effect 
was  reproduced  in  any  degree  in  the  offspring,  the  case  would  be 
relevant;  but  when  the  whole  organism  is  soaked  in  a  poison  the  case 
is  irrelevant.  If  it  could  be  said  that  the  sunshine,  which  brings  about 
sun-burning  in  the  skin,  soaks  through  the  organism  even  to  its  repro- 
ductive cells  and  specifically  affects  them,  in  a  manner  analogous  to 
the  saturating  poison,  we  should  have  a  physiological  basis  for  expect- 
ing the  inheritance  of  sun-burning.  But  we  cannot  make  this  assump- 
tion. We  have  no  warrant  for  believing  that  the  modification  of  a 
part  re-echoes  in  a  definite  specific  way  through  the  organism  until 
even  the  penetralia  of  the  germ-cells  reverberate. 

2.  A  parent  organism  is  poisoned,  and  there  are  structural  results 
of  that  poisoning.  The  offspring  are  born  poisoned,  and  show  similar 
structural  peculiarities.  This  may  be  due  to  the  fact  that  the  germ- 
cells  were  poisoned  along  with  the  parental  body;  but  it  may  also  be 
due,  in  the  case  of  a  mother,  to  a  poisoning  of  the  embryo  before  birth, 
in  a  manner  comparable  to  a  pre-natal  infection. 

3.  In  some  cases — e.g.,  of  alcoholism  in  successive  generations — 
there  may  be  poisoning  of  the  germ-cells  along  with  the  body,  there 
may  be  poisoning  of  the  embryo  before  birth,  and  of  the  infant  after; 
but  it  may  also  be  that  what  is  really  inherited  is  a  specific  degeneracy 
of  nature,  an  innate  deficiency  of  control,  perhaps,  which  led  the  parent 
to  alcoholism,  and  which  may  find  the  same  or  some  other  expression 
in  the  child. 

Cases  are  known  in  which  the  children  of  a  dipsomaniac  father  and 
a  quite  normal  mother  have  exhibited  a  tendency  to  alcoholism, 
insanity,  and  the  like.  In  this  case  the  possibility  of  poisoning  the 
unborn  child  is  eliminated,  but  there  remain  three  possibilities  of 
interpretation — that  there  was  specific  poisoning  of  the  paternal  germ- 
cells;  that  what  was  inherited  was  the  constitutional  weakness  which 
expressed  itself  as  alcoholism  in  the  father;  and  that  there  were  detri- 
mental influences  in  the  early  nutrition,  environment,  education — 
"nurture,"  in  short — of  the  offspring. 

But  while  we  have  admitted  a  good  deal,  we  have  not  admitted 
the  transmissibihty  of  a  particular  structural  modification  brought 
about  in  the  parental  body  as  a  result  of  the  toxin. 

Misunderstanding  VIII. — Failure  to  distinguish  between  the 
possible  inheritance  of  a  particular  modification  and  the  possible  inheri- 
tance of  indirect  results  of  that  modification,  or  of  changes  correlated  with 


ARE  ACQUIRED  CHARACTERS  HEREDITARY?  329 

it.— At  first  sight  this  seems  hair-splittin^^  ])ut  it  is  a  crucial  jioint. 
Through  his  vigorous  exercise  the  blacksmith  develops  a  muscular 
arm  worthy  of  admiration;  the  shoemaker  acquires  skeletal  and 
muscular  peculiarities  less  admirable.  There  are  many  permanent 
and  profound  modifications  associated  with  particular  occupations. 
Are  we  to  believe,  it  is  asked,  that  the  occupation  of  the  parents  has  no 
influence  on  the  offspring?  Are  we  to  believe,  it  is  asked,  that  the 
children  of  soldier,  sailor,  tinker,  tailor,  are  in  no  way  affected  by  the 
parental  functions  ? 

It  would  be  interesting  to  have  precise  data  in  regard  to  this,  l)ut  it 
is  generally  admitted  that  when  parents  have  healthful  occupations 
their  offspring  are  likely  to  be  more  vigorous.  The  matter  is  comi)li- 
cated  by  the  difficulty  of  estimating  how  much  is  due  to  good  nurture 
before  and  after  birth.  It  is  not  unlikely,  too,  that  some  profound 
parental  modifications  may  influence  the  general  constitution,  may 
even  affect  the  germ-cells,  and  may  thus  have  results  in  the  offspring. 
But  unless  the  offspring  show  peculiarities  in  the  same  direction  as  the 
original  modifications,  we  have  no  data  bearing  precisely  on  the  ques- 
tion at  issue. 

A  belief  in  the  inheritance  of  modifications  was  perhaps  expressed 
in  the  old  proverb,  "The  fathers  have  eaten  sour  grapes,  and  the 
chfldren's  teeth  are  set  on  edge" — a  proverb  which  Ezekiel  with  such 
solemnity  said  was  not  any  more  to  be  used  in  Israel.  Now  if  "  setting 
on  edge"  was  a  structural  modification,  and  if  the  children's  teeth  were 
"set  on  edge"  as  their  fathers'  had  been  before  them,  there  would  be  a 
presumption  in  favour  of  the  transmission  of  this  acquired  character, 
though  it  would  be  stiff  necessary  to  inquire  carefully  whether  the 
children  had  not  been  in  the  vineyard  too.  But  if,  as  Romanes  said, 
the  children  were  born  with  wry  necks,  we  should  have  to  deal  with 
the  inheritance  of  an  indirect  result  of  the  parent's  vagaries  of  appetite, 
and  not  with  any  direct  representation  in  inheritance  of  the  particular 
modification  produced  in  the  paternal  dentition. 

Misunderstanding  IX. —  Appealing  to  data  from  not  more  than  two 
generations. — It  has  often  been  pointed  out  that  animals  transported 
to  a  new  country  or  environment  may  exhibit  some  modification 
apparently  the  result  of  the  novel  influence,  and  that  their  offspring 
in  the  same  environment  may  exhibit  the  same  modification  /;/  a 
greater  degree.  Thus  sheep  may  show  a  change  in  the  character  and 
length  of  their  fleece,  and  their  progeny  may  show  the  same  change 
more  markedly. 


330     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

But  it  is  perfectly  clear  that  if  the  evidence  does  not  go  beyond 
this,  nothing  is  proved  that  affects  the  question  at  issue.  It  was  to  be 
expected  that  the  offspring  should  show  the  modification  in  a  more 
marked  degree  than  their  parents  did,  since  the  offspring  were  sub- 
jected to  the  modifying  influences  from  birth,  whereas  their  parents 
were  influenced  only  from  the  date  of  their  importation. 

What  would  be  welcome  is  evidence  that  the  third  generation  is 
more  markedly  modified  than  the  second;  then  there  would  be  data 
worth  considering.  Only  then  would  it  be  necessary  to  consider 
Weismann's  somewhat  subtle  discussion  as  to  the  influence  of  climate. 

THE   INHERITANCE    OR   NON-INHERITANCE   OF   ACQUIRED   CHARACTERS^ 

EDWIN    GRANT   CONKLIN 

Few  questions  in  biology  have  been  discussed  so  fully  and  so 
fruitlessly  as  this.  It  is  a  problem  of  the  greatest  interest  not  only 
to  students  of  biology  but  also  to  sociologists,  educators  and  philan- 
thropists and  yet  it  is  still  to  a  certain  extent  an  unsolved  problem. 

Opinions  of  Lamarck  and  Darwin. — It  is  well  known  that  Lamarck 
taught  that  characters  due  to  desire  or  need,  use  or  disuse,  and  to 
changed  environment  or  conditions  of  life  were  inherited  and  thus 
brought  about  progressive  evolution.  Long  ago  desire  or  need  was 
repudiated  as  a  factor  of  evolution.  Lowell  satirized  it  in  his  Biglow 
Papers  in  these  words: 

"Some  filosifers  think  that  a  fakkilty's  granted 
The  minnit  it's  felt  to  be  thoroughly  wanted. 

That  the  fears  of  a  monkey  whose  holt  chanced  to  fail 
Drawed  the  vertibry  out  to  a  prehensile  tail." 

Darwin  wrote  to  Hooker,  ''Heaven  forfend  me  from  Lamarck's  non- 
sense of  adaptation  from  the  slow  willing  of  animals";  but  although 
he  repudiated  this  feature  of  Lamarckism  he  held  that  characters  due 
to  use  or  disuse  and  to  changed  conditions  of  life  might  be  inherited 
and  he  proposed  his  hypothesis  of  pangenesis  in  order  to  explain  the 
process  of  the  transmission  of  such  characters  to  the  germ  cells. 

Weismann's  theories. — Weismann  introduced  a  new  era  in 
biology  by  denying  the  inheritance  of  all  kinds  of  acquired  characters, 
and  by  challenging  the  world  to  produce  evidence  that  would  stand  a 

*  From  E.  G.  Conklin,  Heredity  and  Environment  (copyright  1919).  Used  by 
special  permission  of  the  publishers,  The  Princeton  University  Press. 


ARE  ACQUIRED  CHARACTERS  HERKDITARV?  331 

rigorous  analysis.  But  Weismann's  greatest  service  lay  in  his  con- 
structive theories  rather  than  in  destructive  criticism;  he  forever 
disposed  of  theories  of  pangenesis  and  the  like  by  showing  that  the 
germ  cells  are  not  built  up  by  contributions  from  the  body  and  that 
characters  are  not  transmitted  from  generation  to  generation;  but 
on  the  other  hand  that  there  is  transmitted  a  germ  plasm  which  is 
relatively  independent  of  the  body  and  which  is  relatively  very  stable 
in  organization.  This  epoch-making  theory  of  Weismann's  has  natu- 
rally undergone  some  changes,  as  the  result  of  new  discoveries. 
It  is  no  longer  believed  that  the  germ  plasm  is  really  independent  of 
the  body,  nor  that  it  is  absolutely  stable,  as  Weismann  at  one  time 
held.  There  is  no  doubt  that  the  germ  cells  and  the  germ  plasm  are 
physiologically  related  to  other  cells  and  to  other  plasms,  and  similarly 
there  is  no  doubt  that  the  germ  plasm  although  very  stable  can  and 
does  change  its  constitution  under  some  rare  conditions.  But  in  the 
main  the  germ  plasm  theory  is  accepted  by  the  great  majority  of 
biologists  to-day,  and  recent  work  in  genetics  and  cytology  has  brought 
many  confirmations  of  this  theory. 

Distinctions  between  hereditary  and  acquired  characters. — As 
long  as  it  was  believed  that  the  developed  characters  of  an  organism 
could  be  transmitted  as  such  to  its  descendants  it  was  customary  to 
speak  of  developed  characters  as  hereditary  or  acquired  and  to  talk  of 
the  inheritance  or  non-inheritance  of  acquired  characters.  This  dis- 
tinction is  not  a  logical  one  for  all  developed  characters  are  invariably 
the  result  of  the  responses  of  the  germinal  organization  to  environ- 
mental stimuli;  and  of  course  no  developed  character  can  be  purely 
hereditary  or  purely  environmental.  But  when  a  given  character 
arises  in  many  individuals  of  the  same  genotype  under  different 
environmental  conditions  it  is  probable  that  heredity,  which  is  the 
constant  factor  in  this  case,  is  also  the  determining  factor  for  that 
character.  On  the  other  hand  if  a  character  develops  in  response  to 
peculiar  stimuli  and  does  not  appear  in  other  individuals  of  the  same 
genotype  in  which  such  stimuli  are  lacking  it  is  said  to  be  an  environ- 
mental or  acquired  character.  In  line,  inherited  characters  are  those 
whose  distinctive  or  differential  causes  are  in  the  germ  cells,  while 
acquired  characters  are  those  whose  differential  causes  are  environ- 
mental. 

Statement  of  problem.— Briefly  stated  the  question  of  the  inheri- 
tance of  acquired  characters  is  this:  Can  the  differential  cause  of  a 
character  be  shifted  from  the  environment  to  the  germ  i)lasm  ?     Can 


332     READINGS  IX  EVOLUTION,  GENETICS,  AND  EUGENICS 

peculiarities  of  the  environment  which  influence  the  development  of 
somatic  characters  so  affect  the  germ  cells  that  they  will  produce  these 
somatic  characters  in  the  absence  of  the  peculiar  environment  ?  Can 
the  characteristics  of  a  developed  organism  enter  into  its  germ  cells 
and  be  born  again  in  the  next  generation  ?  Considering  the  fact  that 
germ  cells  are  cells  and  contain  no  adult  characteristics,  it  seems  very 
improbable  that  any  peculiarity  of  environment  whether  of  nutri- 
tion, use,  disuse  or  injury,  which  brings  about  certain  peculiarities  of 
developed  characters  in  the  adult,  could  so  change  the  structure  of  the 
germ  cells  as  to  cause  them  to  produce  this  same  character  in  subse- 
quent generations  in  the  absence  of  its  extrinsic  cause.  How,  for 
example,  could  defective  nutrition,  which  leads  to  the  production  of 
rickets,  affect  the  germ  cells,  which  contain  no  bones,  so  as  to  produce 
rickets  in  subsequent  generations,  although  well  nourished  ?  Or  how 
can  over-exertion,  leading  to  hypertrophy  of  the  heart,  so  affect  the 
germ  cells  that  they,  in  turn,  would  produce  hypertrophied  hearts  in 
the  absence  of  over-exertion,  seeing  that  germ  cells  have  no  hearts  ? 
Or  how  could  the  loss  or  injury  of  eyes  or  teeth  or  legs  lead  to  the 
absence  or  weakened  development  of  these  organs  in  future  generations, 
seeing  that  inheritance  must  be  through  germ  cells  which  possess  none 
of  these  structures  ? 

Lack  of  evidence  for  inheritance  of  acquired  characters. — But, 
apart  from  these  general  objections  to  the  doctrine  of  the  inheritance 
of  acquired  characters,  there  are  many  special  difficulties.  There  is 
no  conclusive  and  satisfactory  evidence  in  favor  of  such  inheritance. 
Almost  all  the  evidence  adduced  serves  to  show  only  that  characters 
are  acquired,  not  that  they  are  inherited. 

It  is  a  matter  of  common  observation  that  mutilations  are  not 
inherited;  wooden  legs  do  not  run  in  families,  although  wooden  heads 
do.  The  evidence  for  the  inheritance  of  peculiarities  due  to  use  or 
disuse  is  wholly  inconclusive;  for  example,  did  the  giraffe  get  his  long 
neck  because  he  browsed  on  trees,  or  does  he  browse  on  trees  because 
he  has  by  inheritance  a  long  neck  ?  Did  attempts  to  fly  lead  to  the 
development  of  wings  in  birds,  or  do  birds  fly  because  heredity  has 
given  them  wings.?  Did  Hfe  in  caves  make  cave  animals  blind,  or  did 
blind  animals  resort  to  caves  because  the  struggle  for  existence  there 
was  less  severe  for  them  ?  The  evidence  is  in  favor  of  the  second  of 
each  of  these  alternatives  rather  than  of  the  first. 

There  stiU  remains  the  question  of  the  inheritance  of  certain 
characters  due  to  environment,  though  here  also  the  most  clear-cut 


ARE  ACQUIRED  CHARACTERS  HEREDITARY?  333 

evidence  is  against  this  proposition.  That  unusual  conditions  of  food, 
temperature,  moisture,  etc.,  may  affect  the  germ  cells  so  as  to  produce 
general  and  indefinite  variations  in  offspring  is  probable,  but  this  is  a 
very  different  thing  from  the  inheritance  of  acquired  characters.  The 
germ  cells  being  a  part  of  the  parental  organism  may  be  modified  by 
such  changes  in  the  environment  as  affect  the  body  as  a  whole,  they 
may  be  well  nourished  or  starved,  they  may  be  modified  by  changed 
conditions  of  gravity,  salinity,  pressure,  temperature,  etc.,  and  these 
modifications  of  the  germ  cells  probably  lead  to  certain  general  modi- 
fications of  the  adult,  which  may  be  larger  or  smaller,  stronger  or 
weaker,  according  as  the  germ  is  well  or  poorly  nourished,  but  it  is 
incredible  that  the  environment  which  produces  rickets,  or  hyper- 
trophied  heart,  or  loss  of  sight  in  one  generation  should  modify  the 
germ  cells  in  such  a  peculiar  and  definite  way  that  they  should  give 
rise  in  the  next  generation  to  these  particular  peculiarities,  in  the 
absence  of  the  extrinsic  cause  which  first  produced  them.  The 
inheritance  of  acquired  characters  is  incredible,  because  the  egg  is 
a  cell  and  not  an  adult  organism;  and  in  this  case  there  is  no  suffi- 
cient evidence  that  the  thing  which  is  incredible  really  does  happen. 

No  inherited  influence  of  stock  on  graft. — If  specific  changes  of 
environment  produced  specific  changes  in  heredity  we  should  expect 
to  find  that  where  different  plants  or  animals  are  grafted  together  each 
would  modify  more  or  less  the  hereditary  constitution  of  the  other. 
But  this  does  not  occur.  Everybody  knows  that  when  a  branch  of  a 
particular  kind  of  fruit  tree  is  grafted  upon  a  tree  of  a  different  variety 
the  quality  of  the  fruit  borne  by  that  branch  is  not  altered  by  its  close 
union  with  the  new  stock.  The  same  is  true  of  all  forms  of  animal 
grafts.  Harrison  cut  in  two  young  tadpoles  of  two  species  of  frog, 
Rana  syhatica  and  Rana  palustris,  and  spliced  the  anterior  half  of  one 
to  the  posterior  half  of  the  other.  These  frogs  and  their  tadpoles 
differ  in  color  as  well  as  in  other  respects,  R.  syhatica  being  more  deeply 
pigmented  than  R.  palustris.  In  the  grafted  tadpoles  each  half  pre- 
served its  own  peculiarities  even  up  to  the  adult  condition. 

A  still  more  striking  case  of  the  persistence  of  heredity  in  spite  of 
environmental  changes  is  found  in  experiments  in  which  the  ovaries 
are  removed  from  one  variety  of  animal  and  transplanted  to  another 
variety.  Guthrie  made  such  transplation  in  the  case  of  fowls  and 
concluded  that  there  was  some  influence  of  the  foster  mother  upon  the 
transplanted  ovary,  but  Davenport,  who  repeated  his  experiments,  was 
unable  to  confirm  his  results.     Finally  Castle  and  Phillips  furnished 


334      READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

the  most  conclusive  demonstration  that  the  hereditary  character- 
istics of  the  transplanted  ova  are  in  no  wise  changed  by  the  foster 
mother.  They  removed  the  ovary  from  a  pure  black  guinea-pig  and 
put  it  in  the  place  of  the  ovary  of  a  pure  white  animal.  After  recover- 
ing from  the  operation  this  white  female  with  the  "black"  ovary  was 
bred  to  a  pure  white  male.  Three  litters  of  offspring  from  these 
parents  were  all  pure  black.  Although  both  parents  were  pure  white 
all  the  offspring  of  the  Fi  generation  were  black  because  they  came 
from  ''black''  eggs  and  black  is  dominant  over  white.  The  fact  that 
these  "black"  eggs  developed  in  the  body  of  a  white  female  did  not  in 
the  least  change  their  hereditary  constitution. 

Dominants  and  recessives  remain  pure. — A  still  more  intimate 
union  takes  place  when  the  dominant  and  recessive  characters  come 
together  in  any  zygote.  These  characters,  or  rather  the  factors  which 
determine  them,  may  be  intimately  associated  in  every  cell  of  the 
organism  throughout  an  entire  generation  and  yet  we  may  get  a  clean 
separation  of  these  characters  in  the  next  generation;  in  many  cases 
neither  the  dominant  nor  the  recessive  character  has  been  at  all  modi- 
fied by  its  most  intimate  association  with  the  other. 

Climatic  effects  not  inherited. — A  striking  instance  of  the  purely 
temporary  effect  of  the  environment  and  of  the  long  persistence  of 
hereditarv  constitution  amidst  new  environmental  conditions,  which 
have  greatly  changed  the  appearance  of  the  developed  organisms,  is 
found  in  the  case  of  alpine  plants.  Nageli  says  that  such  plants,  which 
have  preserved  the  characters  of  high  mountain  plants  since  the  ice 
age,  lose  these  characters  perfectly  during  their  first  summer  in  the 
lowlands. 

Summary. — If  acquired  characters  were  really  inherited  we  should 
expect  to  find  many  positive  evidences  of  this  instead  of  a  few  sporadic 
and  doubtful  cases.  In  particular  why  do  we  not  find  in  plant  or 
animal  grafting  that  the  influence  of  the  stock  changes  the  hereditary 
potencies  of  the  graft  ?  Why  do  we  not  find  that  transplanted  ovaries 
show  the  influence  of  the  foster  mother  as  Guthrie  supposed — a  thing 
which  has  been  disproved  by  Castle  ?  Why  do  dominant  and  recessive 
characters  remain  pure,  even  after  their  intimate  union  in  a  hybrid,  so 
that  pure  dominants  and  pure  recessives  may  be  obtained  in  subse- 
quent generations  from  this  mixture  ?  Why  does  every  child  have  to 
learn  anew  what  his  parents  learned  so  laboriously  before  him  ?  Even 
the  strongest  defenders  of  the  inheritance  of  acquired  characters  are 
constrained  to  admit  that  it  occurs  only  sporadically  and  excep- 
tionally. 


ARE  ACQUIRED  CHARACTERS  HEREDITARY?  335 

Neo-Lamarckism.— Many  modifications  of  the  Lamarckian 
hypothesis  of  the  inheritance  of  acquired  characters  have  been  pro- 
posed in  recent  years.  Foremost  among  those  are  the  '"mneme" 
theory  of  Semon  and  the  "  centro-epigenesis  "  theory  of  Rignano.  To 
Semon  as  to  many  other  biologists  the  apparent  resemblance  between 
memory  and  heredity  has  seemed  significant,  and  this  furnishes  the 
basis  of  his  theory.  Semon  holds  that  every  condition  of  life,  every 
functional  activity  of  an  organism  leaves  a  permanent  record  of  itself 
in  what  he  calls  an  "engramme."  If  these  conditions  or  activities 
are  long  continued  their  engrammes  are  heaped  up  and  affect  heredity. 
Semon  does  not  ask  if  "acquired  characters"  are  inherited,  but  rather 
"Are  the  hereditary  potencies  of  the  germ  cells  altered  by  stimuli 
acting  on  the  parental  body?"  This  is  a  very  different  thing  from 
the  inheritance  of  a  particular  acquired  character,  and  there  is  some 
evidence  that  such  stimuli  may  in  rare  instances  produce  changes  in 
the  hereditary  constitution  of  the  germ  plasm  though  these  evidences 
are  by  no  means  conclusive. 

Temporary  effects  of  environment;  "induction." — On  the  other 
hand  certain  changes  may  be  produced  in  germ  cells  or  embryos  which 
last  for  only  a  generation  or  two  and  then  disappear.  It  is  well  known 
that  plants  grown  in  poor  soil  are  smaller  and  produce  smaller  seeds 
than  those  grown  in  good  soil,  and  De  Vries,  Bauer  and  Harris  find 
that  such  seeds  produce  smaller  plants  having  smaller  seeds  than  do 
seed  of  normal  size.  This  is  an  after  effect  of  poor  nutrition  which 
changes  the  amount  of  food  material  in  the  seeds  and  through  this  the 
size  of  the  plant  which  develops  from  the  seed,  but  it  does  not  change 
the  hereditary  constitution.  Woltereck  found  that  in  Daphnia  there 
is  an  after  effect  of  cold  lasting  for  one  or  two  generations,  and  this  he 
calls  "induction,"  when  the  effect  lasts  for  one  generation,  or  "pre- 
induction  "  when  it  lasts  for  two  or  three  generations.  Whitney  found 
that  rotifers  poisoned  with  alcohol  were  weaker  in  resistance  to  copper 
salts  and  were  less  fertile  than  others,  and  when  brought  back  to 
normal  conditions  the  first  generation  was  weak  but  the  second  was 
normal.  On  the  other  hand  Stockard  finds  that  the  injurious  effects 
of  alcohol  on  guinea  pigs  persist  through  two  or  more  generations.  In 
man  alcohol  may  have  an  "induction"  effect  on  offspring,  but  fortu- 
nately it  does  not  seem  to  alter  hereditary  constitution.  Probably  of  a 
similar  character  are  Sumner's  results;  he  found  that  mice  raised  in  the 
cold  have  shorter  tails  than  those  raised  in  higher  temperatures  and  this 
modified  character  appears  in  the  next  generation.  If  this  is  an  after 
effect  or  "induction"  it  should  disappear  in  the  following  generations. 


336     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

Kammerer  found  that  salamanders  with  black  and  yellow  spots 
when  reared  on  yellow  soil  gradually  lose  their  black  color,  becoming 
more  \ellow,  and  their  young  continue  to  grow  more  yellow  until 
finally  almost  all  black  may  disappear.  The  offspring  of  such  sala- 
manders are  said  to  be  more  yellow  than  normal;  but  this  work  has 
been  called  in  question  and  needs  confirmation.  Even  if  confirmed 
the  result  may  be  an  after  effect  or  "induction"  which  would  soon 
disappear  under  usual  conditions,  and  there  is  no  evidence  that  it  is 
really  inherited. 

Such  cases  are  not  instances  of  true  inheritance;  they  do  not 
signify  a  change  in  the  hereditary  constitution  but  an  influence  on  the 
germ  cells  of  a  nutritive  or  chemical  sort  comparable  with  what  takes 
place  when  fat  stains  are  fed  to  animals;  the  eggs  of  such  animals  are 
stained,  and  the  young  which  develop  from  such  eggs  are  also  stained, 
though  the  germinal  constitution  rem  ins  unchanged.  The  very  fact 
that  the  changed  condition  is  reversible  and  that  it  disappears  within 
a  short  time  is  evidence  that  it  is  not  really  inherited. 

In  conclusion:  (i)  Developed  characters,  whether  "acquired" 
or  not,  are  never  transmitted  by  heredity,  and  the  hereditary  constitu- 
tion of  the  germ  is  not  changed  by  changes  in  such  characters.  (2) 
Possibly  environmental  stimuli  acting  upon  germ  cells  at  an  early 
stage  in  their  development  may  rarely  cause  changes  in  hereditary 
constitution,  but  changes  produced  in  somatic  cells  do  not  cause 
corresponding  changes  in  the  hereditary  constitution  of  the  germ  cells. 
(3)  Germ  cells  like  somatic  cells  may  undergo  modifications  which  are 
not  hereditary;  if  starved  they  may  produce  stunted  individuals  and 
this  effect  may  last  for  two  or  three  generations;  they  may  be  stained 
with  fat  stains  and  the  generation  to  which  they  give  rise  be  similarly 
stained;  they  may  be  poisoned  with  alcohol  or  modified  by  tempera- 
ture and  such  influence  be  carried  over  to  the  next  generation  without 
becoming  hereditary.  All  such  cases  are  known  as  "induction"  and 
many  instances  of  the  supposed  inheritance  of  acquired  characters 
come  under  this  category.  (4)  Environment  may  profoundly  modify 
individual  development  but  it  does  not  generally  modify  heredity. 


THE   OTHEl^    SIDE   TO   THE   QUESTION 

[It  will  have  been  noted  that  the  chief  objection  to  the  idea  of  the 
possibility  of  acquired  characters  being  inherited  comes  to  us  as  a 
heritage  of  the  rather  extreme  Weismannian  concept  of  the  "germ 


ARE  ACQUIRED  CHARACTERS  HEREDITARY?  337 

plasm."  According  to  this  view  as  brought  out  Ijy  Professor  Guyer 
(p.  296),  there  is  an  unbroken  continuity  from  generation  to  generation 
of  the  germ  plasm.  Germ  cells  are  thought  of  as  remaining  entirely 
undifferentiated  for  any  somatic  function  and  as  therefore  capable  of 
starting  at  the  beginning  to  develop  a  new  individual.  The  germ  cell 
is  supposed  to  be  "set  apart  at  an  early  period  in  a  given  individual; 
it  takes  no  part  in  the  formation  of  the  individual's  body,  but  remains 
a  slumbering  mass  of  potentialities  which  must  bide  its  time  to  awaken 
into  expression  in  a  subsequent  generation." 

Physiologists  object  to  this  idea  that  the  germ  cells  are  so  dis- 
tinctly different  from  body  cells  and  that  they  are  so  insulated,  as  it 
were,  from  the  soma  as  to  be  immune  to  any  changes  that  may  affect 
the  latter.  Two  kinds  of  data  are  offered  in  opposition  to  this  con- 
cept. A  few  observers,  notably  Professor  C.  M.  Child,  have  described 
cases  in  which  somatic  cells,  that  already  had  become  differentiated 
as  primitive  muscle  cells,  lost  their  differentiation  and  returned  to  a 
germinal  condition.  If  this  kind  of  thing  were  general,  and  it  is 
probably  not,  germ  cells  might  conceivably  be  produced  from  func- 
tioning soma  cells  and  might  therefore  furnish  a  mechanism  for  the 
transmission  of  the  effects  of  use  and  disuse.  It  should  be  empha- 
sized, however,  that,  among  animals  at  least,  there  is  extremely  little 
evidence  in  support  of  the  idea  that  differentiated  body  cells  give  rise 
to  germ  cells. 

Among  plants,  however,  a  different  situation  prevails.  In  the 
Begonia,  for  example,  any  part  of  a  plant  if  cut  off  is  capable  of  pro- 
ducing a  whole  new  plant.  Even  a  purely  vegetative  organ  like  a  leaf, 
if  cut  off  and  partially  buried  in  soil,  will  bud  off  a  new  plant  which 
will  produce  flowers  with  perfectly  typical  germ  cells.  We  have  to 
admit,  in  this  case,  either  that  leaf  tissues  contain  undifferentiated  germ 
cells  or  that  somatic  tissues  give  rise  to  germ  cells.  The  first  alterna- 
tive is  in  harmony  with  the  germ-plasm  hypothesis,  the  second  is 
the  preferred  view  of  the  opponents  of  this  hypothesis. 

Among  animals,  as  for  example  annelid  worms,  it  is  quite  common 
to  find  the  germ  cells  aggregated  in  a  few  segments  (^f  the  body.  If  a 
part  of  the  body  in  which  there  are  no  recognizable  germ  cells  be  cut 
off,  it  will,  under  proper  conditions,  regenerate  the  lost  jxirts  and 
become  a  complete  worm  with  functional  germ  cells.  The  same 
alternative  explanations  that  were  offered  for  the  Begonia  case  apply 
equally  well  here.  Numerous  other  cases  of  the  same  sort  are  well 
known  to  all  zoologists.     To  the  advocate  of  the  "  germ-j^lasm  "  theory 


338      READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

they  offer  no  difficulties  because  he  can  always  fall  back  upon  the 
statement  that  there  is,  among  the  lower  forms  at  least,  reserve  germ 
plasm  equally  distributed  over  the  whole  body  ready  to  differentiate 
into  definite  germ  cells  when  needed.  This  type  of  appeal  is  abhor- 
rent to  the  physiologist,  and  with  some  justification,  for  it  really 
begs  the  question  by  assuming  that  any  cell  that  is  capable  of  form- 
ing germ  cells  belongs  to  the  more  or  less  sacred  lineage  of  germ  plasm. 

If  we  confine  the  application  of  the  germ-plasm  idea  to  the  higher 
animals,  such  as  vertebrates  and  insects,  we  w^ould  obviate  these  chief 
objections,  and  the  present  writer  would  take  the  view  that  it  is  only 
among  the  upper  ranges  of  highly  specialized  animals  that  the  con- 
tinuity of  the  germ -plasm  concept  holds  solidly. 

Another  chief  objection  to  the  germ-plasm  system  has  to  do  with 
the  supposed  insulation  or  apartness  of  the  germ  plasm.  Physiolo- 
gists have  found  that  there  is  an  extremely  intimate  correlation  in 
function  between  practically  all  parts  of  a  living  organism.  Many 
of  the  structures,  such  as  the  rudimentary  pituitary  body,  the  thyroids, 
the  adrenal  body,  and  various  other  bodies  whose  function  was  long 
unknown,  have  now  been  shown  to  exercise  a  profound  effect  on  the 
development  of  the  whole  body.  Since  practically  all  tissues  are 
known  to  affect  at  least  some  other  tissues,  is  it  likely,  the  physiologist 
asks,  that  none  of  the  other  tissues  affect  the  germinal  tissues  ?  The 
organism  is  to  be  viewed,  it  is  said,  not  as  a  collection  of  independently 
functioning  parts,  but  as  a  single  coherent  unit.  On  this  view  no 
tissue  can  be  thought  of  as  beyond  the  influence  of  organic  changes. 

The  classic  argument  of  the  Weismannians  was  that  we  can  con- 
ceive of  no  mechanism  by  means  of  which  somatic  changes  can  be  carried 
back  into  the  germ  cells,  and  therefore  there  is  no  such  mechanism. 
Now  the  fallacy  of  this  argument  is  obvious;  even  if  we  could  con- 
ceive of  no  suitable  mechanism  for  this  purpose,  this  does  not  preclude 
the  existence  of  such  a  mechanism.  Moreover,  according  to  Professor 
Guyer,  just  such  a  mechanism  actually  exists,  as  will  be  brought  out  in 
the  following  quotation  from  one  of  his  recent  publications. — Ed.] 

A  POSSIBLE  MECHANISM  EOR  THE  TRANSMISSION  OF 
ACQUIRED  CHARACTERS' 

MICHAEL   F.    GUYER 

Some  selectionists  glibly  assert  that  new  characters  arise  as  the 
result  of  spontaneous  changes  in  the  germ.     What  is  meant  by  this  ? 

^  From  M.  F.  Guyer,  "Immune  Sera  and  Certain  Biological  Problems," 
American  Naturalist^  Vol.  LV  (192 1). 


ARE  ACQUIRED  CHARACTERS  HEREDITARY?  339 

Just  what  is  a  spontaneous  change  ?  No  one  has  ever  succeeded  in 
telling  us.  And  we  may  suspect,  though  perhaps  it  is  heresy  to  do  so, 
that  it  is  a  well-sounding  phrase  that  is  the  equivalent  of  the  three 
words,  "I  don't  know."  Unwilling  to  admit  of  the  modifying  inlluence 
of  external  agencies  on  the  germ,  such  theorists  resort  to  the  fiction 
of  a  spontaneous  change.  Coleridge  somewhere  has  said,  "What's 
gray  with  age  becomes  religion."  We  have  toyed  so  long  with  this 
idea  of  germinal  continuity  and  the  invulnerability  of  the  germ,  that  it 
has  become  for  some  of  us  wellnigh  sacrosanct.  Living  matter  is 
living  matter  wherever  it  may  be  found,  but  when  it  happens  to  be  in 
the  germ-cells,  verily,  ''this  corruptible  has  put  on  incorruption  and 
this  mortal  immortality"! 

Now,  no  one  to-day,  qualified  by  his  knowledge  of  embryology 
and  genetics  to  the  right  of  an  opinion,  would,  I  think,  deny  that  the 
new  organism  is  in  the  main  the  expression  of  what  was  in  the  germ- 
line,  rather  than  of  what  it  got  directly  from  the  body  of  its  parents, 
but  does  this  fact  necessarily  carry  with  it  the  implication  that  the 
germ  is  insusceptible  to  modification  from  without  ?  Is  not  the  serum 
of  organisms  with  blood  or  lymph  an  excellent  medium  through  which 
external  influences  may  operate  upon  it  ?  Is  it  not  more  reasonable 
to  postulate  the  origination  of  germinal  changes  through  some  such 
mechanism  as  this  than  to  attribute  it  to  mysterious  ''spontaneous 
changes" ? 

With  such  thoughts  in  mind  I  and  my  research  associate.  Dr. 
E.  A.  Smith,  set  about  making  various  tests.  Without  attempting 
to  tell  you  of  our  as  yet  unsuccessful  attempts  to  secure  cytolysins 
which  will  operate  in  the  developmental  stages  of  such  periodically 
renewed  structures  as  feathers,  or  to  weary  you  with  the  history  of  our 
various  other  failures — of  which  there  are  an  abundance — I  wish  to 
speak  briefly  about  certain  antenatal  effects  we  secured  in  rabbits  by 
means  of  fowl-serum  sensitized  against  rabbit  crystalline  lens,  and  of 
the  fact  that  such  induced  defects  may  become  heritable. 

The  crystalline  lens  of  the  rabbit  was  selected  as  antigen,  and  fowls 
as  the  source  of  the  antibodies.  The  lenses  of  newly  killed  rabbits 
were  pulped  thoroughly  in  a  mortar  and  diluted  with  normal  saline 
solution.  About  four  cubic  centimeters  of  this  emulsion  was  then 
injected  intraperitoneally  or  intravenously  into  each  of  several  fowls. 
Four  or  five  weekly  treatments  with  such  lens-emulsions  were  given. 
Then  a  week  or  ten  days  after  the  last  injection  the  blood-serum  of 
one  or  more  of  the  fowls  was  used  for  injection  into  pregnant  rabbits. 
The  rabbits  had  been  so  bred  as  to  have  the  young  advanced  to  about 


340     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

the  tenth  day  of  pregnancy,  since  from  the  tenth  to  the  thirteenth  day 
seems  to  be  a  particularly  important  period  in  the  development  of  the 
lens.  It  is  then  growing  rapidly  and  becomes  surrounded  by  a  rich 
vascular  network  that  later  disappears.  From  four  to  seven  cubic 
centimeters  of  the  sensitized  fowl-serum  were  injected  intravenously 
into  the  pregnant  rabbits  at  intervals  of  two  .or  three  days  for  from 
ten  days  to  two  weeks.  Several  rabbits  died  from  the  treatment  and 
many  young  were  killed  in  utero  Of  sixty-one  surviving  young  from 
mothers  thus  treated,  four  had  one  or  both  eyes  conspicuously  defect- 
ive and  five  others  had  eyes  which  were  clearly  abnormal.  It  is 
possible  that  still  others  wxre  more  or  less  affected,  since  we  judged 
only  by  obvious,  visible  effects.  We  found  later  in  some  of  the 
descendants  of  these  individuals  that  rabbits  which  passed  for  normal 
during  their  earher  months  subsequently  manifested  traces  of  defects 
in  their  lenses  or  in  other  parts  of  the  eye. 

The  commonest  abnormality  seen  in  both  the  original  subjects 
and  in  their  descendants  was  partial  or  complete  opacity  of  the  lens, 
usually  accompanied  by  reduction  in  size.  Other  defects  were  cleft 
iris,  persistent  hyaloid  artery,  bluish  or  silvery  color  instead  of  the 
characteristic  red  of  the  albino  eye,  microphthalmia  and  even  almost 
complete  disappearance  of  the  eyeball.  Taking  into  account  the 
method  of  enbryological  development,  however — the  relation  of  lens, 
optic  cup,  and  choroid  fissure — the  defects  are  probably  all  attributable 
to  the  early  injury  of  the  lens.  In  some  cases,  both  among  originals 
and  descendants,  an  eye  microphth.ilmic  at  birth  may  undergo  fur- 
ther degeneration  such  as  collapse  of  the  ball  and  what  appears  to '  e  a 
resorption  as  if  some  solvent  wxre  operating  upon  it.  The  eyes  of  the 
mothers  apparently  remained  unaffected.  This  is  probaLly  due  to 
the  fact  that  the  lens  tissue  of  the  adult  rabbit  is  largely  avascular 
and  therefore  did  not  come  into  contact  with  the  injected  anti- 
bodies. 

That  the  changes  in  the  eyes  of  the  fetuses  resulted  from  the  action 
of  lens  antibodies  is  indicated  by  the  fact  that  in  not  one  of  the  forty- 
eight  controls  obtained  from  mothers  which  had  been  treated  with 
unsensitized  fowl-serum  or  with  fowl-serum  sensitized  to  rabbit  tissue 
other  than  lens,  was  there  evidence  of  eye-defects,  and  L  may  add, 
that  among  the  hundred  or  more  young  obtained  later  from  mothers 
which  were  being  experimented  upon  with  various  types  of  sera  or 
protein  extracts,  for  other  purposes,  not  a  single  case  of  eye-defect 
has  appeared. 


ARE  ACQUIRED  CHARACTERS  HEREDITARY?  341 

As  already  stated,  once  the  anomaly  is  secured  it  may  Ijc  trans- 
mitted to  subsequent  generations  through  breeding.  So  far  we  have 
succeeded  in  passing  it  to  the  eighth  generation  without  any  other  than 
the  original  treatment.  The  imperfection,  indeed,  tends  to  become 
worse  in  succeeding  generations  and  also  to  occur  in  a  proportionately 
greater  number  of  young.  Though  not  analyzed  completely  as  to  its 
exact  mode  of  inheritance,  it  has  in  general,  the  characteristics  of  a 
Mendelian  recessive.  Like  such  anomalies  as  brachydactyly  or  Poly- 
dactyly in  man,  the  transmission  is  not  infrequently  of  an  irregular, 
unilateral  type,  sometimes  only  the  right,  at  others  only  the  left  eye 
showing  the  defect.  In  the  later  generations,  probably  in  some 
measure  as  the  result  of  selective  breeding,  there  is  an  increasing  num- 
ber of  young  which  have  both  eyes  affected. 

To  determine  whether  the  reappearance  of  the  defect  was  due 
merely  to  the  passing  on  of  antibodies  or  kindred  substances  from  the 
blood  stream  of  the  mother,  or  to  true  inheritance,  we  mated  defective- 
eyed  males  to  normal  females  from  strains  of  rabbits  unrelated  to  our 
defective-eyed  stock.  The  first  generations  produced  in  this  way 
were  invariably  normal-eyed,  but  when  females  of  this  generation 
were  mated  to  defective-eyed  males  again,  we  secured  defective-eyed 
young  after  the  manner  of  an  extracted  Mendelian  recessive.  It  is 
obvious  that  in  such  cases  the  abnormality  could  only  have  been 
conveyed  through  the  germ-cells  of  the  male,  and  that  it  is,  therefore, 
an  example  of  true  inheritance.  Subsequent  matings  have  shown  that 
these  young  transmit  the  eye-anomalies  as  effectively  as  do  individuals 
of  the  original  lines.  A  new  strain  of  defective-eyed  young,  estab- 
lished about  the  time  our  original  paper  went  to  press,  is  also  flourish- 
ing and,  as  regards  transmission  of  the  defect,  seems  to  differ  in  no 
way  from  the  earlier  stock. 

But  now,  let  us  inquire  as  to  where  all  this  leads.  Without  enter- 
ing into  a  discussion  of  just  what,  serologically,  is  taking  place  in  the 
body  or  in  the  germ  of  fetuses  borne  by  the  lens-treated  mothers,  the 
point  I  wish  to  emphasize  is  that  a  certain  specific  effect  has  been  pro- 
duced; and,  what  is  of  greater  moment,  once  the  condition  is  estab- 
lished it  may  be  not  merely  transmitted,  but  inherited.  Whether  the 
lens  of  the  uterine  young  is  first  changed  and  then  in  turn  induces  a 
change  in  the  lens-producing  antecedents  in  the  germ-cells  of  these 
young,  or  whether  the  specific  antibody  simultaneously  affects  the 
eyes  and  the  germ-cells  of  the  young  is  not  clear.  In  any  event  it 
is  evident  that  there  is  some  constitutional  identity  between  the 


342     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

substance  of  the  mature  organ  in  question  and  the  material  ante- 
cedents of  such  an  organ  as  it  exists  in  the  germ. 

Biologically  considered,  the  most  significant  fact  is  that  specific 
antibodies  can  induce  specific  modifications  in  the  germ-cell.  Whether 
these  antibodies  are  transmitted  from  the  mother's  blood  or  engen- 
dered in  that  of  the  young  would  seem  to  be  of  secondary  importance. 
It  stands  to  reason  that  antibodies  originated  in  an  animal's  own  blood 
will  modify  germinal  factors  if  corresponding  antibodies  introduced 
from  without  can  accomplish  this. 

The  whole  question  as  to  how  important  such  a  fact  may  be  in 
contributing  to  an  understanding  of  the  causes  of  the  germinal  changes 
in  organisms  in  general,  which  lead  to  variation  and  evolution,  hinges 
on  the  question  of  whether  changes  in  an  animal's  tissue  will  induce 
the  formation  of  antibodies  or  kindred  active  substances  in  its  own 
body.  We  have  steadily  accumulating  evidence  that  such  reactions 
do  occur. 

In  our  own  laboratory,  for  example,  after  many  attempts  we  have 
succeeded  in  securing  a  defective-eyed  young  rabbit  from  a  mother 
of  normal  stock  by  injecting  her  repeatedly  with  pulped  rabbit  lens 
before  and  during  pregnancy.  Since  the  young  rabbit  in  question  has 
both  eyes  badly  affected  there  can  be  no  question  that  a  rabbit  can 
build  antibodies  against  rabbit-tissue  which  are  as  effective  as  those 
engendered  in  a  foreign  species  such  as  the  fowl.  We  have  likewise 
found  it  relatively  easy  to  secure  spermatoxins  by  directly  injecting 
rabbits,  both  male  and  female,  with  rabbit  spermatozoa.  Moreover, 
a  given  male  will  develop  antibodies  against  his  own  spermatozoa  if  he 
is  injected  intravenously  with  the  latter. 

We  are  also  securing  evidence  that  serologic  reactions  induced  in 
the  fetus  through  operations  on  the  mother  are  not  mere  passive  trans- 
missions, but  may  become  actively  participated  in  by  the  tissues  of  the 
fetus.  For  example,  female  rabbits  sensitized  with  typhoid  vaccine 
followed  by  living  typhoid  germs  may  transmit  to  their  young  and 
even  to  their  grand  descendants  the  ability  to  agglutinate  typhoid 
bacilli  in  serum  diluted  from  60  to  160  times.  From  the  standpoint 
of  heredity  we  have  no  reason  so  far  for  maintaining  that  this  is 
anything  but  placental  transmission,  though  we  are  going  to  practice 
immunization  generation  after  generation  for  a  number  of  generations 
to  determine  if  a  truly  hereditary  immunity  will  be  established.  How- 
ever, facts  have  come  to  light  which  show  that  there  is  more  concerned 
in  the  operation  than  a  mere  transfer  of  antibodies  from  mother  to 


ARE  ACQUIRED  CHARACTERS  HEREDITARY?  343 

fetus.  For  instance,  the  blood  of  young  shortly  after  birth  may  show 
a  higher  titer  than  that  of  the  mother.  Again,  after  two  or  three 
months  of  development  the  young  of  certain  of  the  sensitized  mothers 
have  shown  a  rather  sudden  rise  in  titer,  much  above  that  of  the 
mothers.  In  such  cases  it  would  seem  that  some  mechanism  in  the 
young  rabbit  itself  is  constructing  antibodies  which  supplement  those 
passively  derived  from  the  mother.  Possibly  in  the  process  of  develop- 
ment some  organ  important  in  such  reactions  just  came  into  function- 
ing. If  this  is  true  further  experiments  may  throw  some  light  on  the 
perplexing  question  of  the  source  or  sources  of  the  antibodies  in  an 
animal.  After  a  few  weeks,  in  such  cases,  the  titer  drops  back  again. 
In  still  another  set  of  experiments  we  found  that  young  from  a  sen- 
sitized mother,  when  nursed  by  a  normal  untreated  mother,  retained  a 
fairly  high  titer  for  several  months  and  even  showed  the  rise  of  titer 
mentioned.  On  the  other  hand,  young  of  an  untreated  mother  when 
nursed  by  a  sensitized  mother  acquired  a  fairly  high  titer  from  the 
milk  of  the  foster  mother  but  lost  it  rapidly  after  weaning  time.  Thus 
there  are  evidently  constitutional  factors  operative  in  the  young  which 
have  acquired  their  immunity  through  the  placenta  which  are  absent 
in  the  young  whose  antibodies  were  conveyed  through  food. 

That  changes  in  the  blood  serum  may  be  caused  by  changed  con- 
ditions in  the  tissues  is  further  attested  by  many  facts.  For  example, 
in  pregnancy,  the  newly  forming  placenta  may  set  free  cells  or  cell- 
products  which,  sometimes  at  least,  cause  changes  in  the  blood-serum 
of  the  mother,  though  the  exact  nature  of  these  changes  is  in  dispute. 
Romer,  using  the  complement-fixation  technique,  found  that  the 
serum  of  adult  human  beings  may  possess  antibodies  for  their  own  lens 
proteins.  Bradley  and  Sansum,  employing  anaphylactic  reactions, 
found  that  guinea-pigs  injected  with  guinea-pig  tissue-proteins  (liver, 
heart,  muscle,  testicle,  kidney)  develop  immunity  reactions.  Again 
during  the  late  war,  the  type  of  toxic  action  to  which  anaphylactic 
shock  conforms  was  found  to  exist  after  extensive  injury  of  the  soft 
tissues.  It  resulted  apparently  from  the  absorption  of  poisonous 
substances  of  tissue  origin  into  the  circulation.  In  fact,  various  cells 
and  tissues  when  injured  liberate  such  poisons,  and  even  blood  in  clot- 
ting is  known  to  acquire  a  transient  toxicity  of  this  type. 

With  facts  such  as  these  before  us,  is  it  not  a  rational  hypothesis 
to  assume  that  changes  in  various  parts  of  a  body  may  on  occasion 
influence  the  representatives  of  such  parts  in  the  germ-cells  borne  by 
that  body?     This  appears  all  the  more  probable  when  we  recall  the 


344     READINGS  IN  EVOLUtlON,  GENETICS,  AND  EUGENICS 

facts  learned  from  a  study  of  precipitins  and  of  anaphylaxis  that  each 
species  of  animal  has  a  thread  of  fundamental  similarity  underlying 
the  proteins  of  all  its  tissues.  There  is  no  reason  to  suppose  that  germi- 
nal tissue  forms  an  exception.  The  further  fact  that  homologous 
tissues,  though  existing  in  different  species  of  animals,  possess  similar 
chemical  characteristics,  shows  that  to  get  an  effect  there  need  not 
be  absolute  chemical  identity  between  the  substance  of  such  a  tissue 
as  the  lens  and  the  germinal  constituents  of  which  it  is  the  expres- 
sion.    And  if  this  is  true  for  lens,  why  not  for  other  tissues  ? 

The  blood-serum  of  any  organism  with  blood  thus  affords  a  means 
of  conveying  the  effects  of  changes  in  a  parental  organ  to  the  germ- 
cell  which  contains  the  antecedent  of  such  an  organ.  As  long  as  there 
is  little  change  in  the  somatic  element  its  germinal  correlative  would 
presumably  remain  constant,  but  any  alternations  of  the  soma  which 
give  rise  to  the  formation  of  anti-bodies  or  other  active  agents,  par- 
ticularly if  long  continued,  might  induce  changes  in  the  germ.  Such  a 
h}^othesis  would  seem  to  be  plausible  at  least  in  accounting  for 
degenerative  changes  such  as  the  deterioration  of  eyes  in  such  forms 
as  the  mole,  or  in  fact,  in  the  formation  of  vestigial  organs  in  general. 

On  the  other  hand,  there  is  no  reason  to  infer  that  changes  induced 
in  the  blood-serum  may  not  also  be  instrumental  in  leading  to  pro- 
gressive as  well  as  regressive  evolution.  If  we  may  have  germinally 
destructive  constituents  engendered  in  the  blood  there  is  no  valid 
reason  for  supposing  that  we  may  not  also  have  constructive  ones. 
When  we  learn  more  about  what  initiates  and  promotes  growth  in  a  part 
through  exercise,  or  what  causes  hypertrophy  of  an  organ,  we  may 
likewise  find  how  corresponding  germinal  antecedents  of  that  part 
may  be  enhanced.  Until  such  time  we  shall  probably  remain  in  the 
dark  regarding  the  mechanism  of  progressive  germinal  changes.  As 
already  indicated,  in  the  hormones  and  chalones  we  have  a  wonderful 
series  of  secretions  normally  circulating  in  the  blood  and  maintaining 
general  physiological  equilibrium.  That  reciprocal  stimulations  of 
various  organs  occur  by  this  means  is  a  well-established  fact.  Hyper- 
trophy or  atrophy  of  an  endocrine  gland  may  produce  pronounced 
effects  in  the  furthermost  reaches  of  the  body.  Again  we  may  inquire, 
is  it  reasonable  to  suppose  that  the  germinal  tissues  will  be  inviolate 
to  all  this  ebb  and  flow  of  chemical  influence  ?  Should  we  not  expect 
specific  reactions  or  selections  here  no  less  surely  than  in  other  tissues  ? 
Destruction  of  the  pars  buccalis  of  the  hypophysis  in  the  frog-tadpole 
will  cause  profound  alteration  in  other  endocrine  organs  such  as  the 


ARE  ACQUIRED  CHARACTERS  HEREDITARY?  345 

adrenals  and  thyroids,  will  retard  the  growth  rate,  render  the  entire 
organism  albinous,  and  produce  in  the  individual  pigment  cells  a  con- 
dition of  sustained  contraction.  Shall  we  conclude  that  such  a  far- 
reachin'T  influence  as  this,  particularly  in  a  developing  organism,  will 
pass  the  germ-cells  by  unscathed  ? 

Similarly,  growth  in  man  is  known  to  be  controlled  by  a  pituitary 
secretion  that  is  carried  by  the  blood  to  the  various  organs.  The 
normal  development  of  secondary  sexual  characters  is  determined  by 
products  from  the  testes  or  ovaries,  and  the  activities  of  the  generative 
organs  themselves  are  intimately  associated  with  the  functioning  of  the 
adrenal  and  other  glands.  The  periods  of  ovulation  are  inhibited  by 
secretions  from  the  corpus  luteum;  lactation  is  incited  by  products  of 
the  corpus  luteum,  the  involuting  uterus  and  the  placenta;  the  car- 
bohydrate metabolism  in  the  liver  and  even  in  the  most  distant 
muscles  is  profoundly  influenced  by  substances  formed  in  the  pan- 
creas; the  pancreas,  liver,  and  intestinal  glands  are  set  to  secreting 
through  the  stimulus  of  a  product  fornied  in  the  duodenal  and  jejunal 
mucosae.  And  still  others  of  such  remarkable  interrelations  can 
be  cited. 

Truly  one  may  pronounce  that  social  complex  of  reciprocating 
individuals  termed  cells  w^hich  make  up  an  organism,  ''members  one 
of  another."  And  with  all  of  these  co-operative  activities  of  the 
various  parts  of  the  body  it  is  inconceivable  to  me,  at  least,  that  the 
germ-cells,  bathed  in  the  same  fluid,  nourished  with  the  same  food, 
stand  wholly  apart. 

May  we  not  surmise  then  that  as  regards  inheritance  and  evolu- 
tion, Lamarck  was  not  wholly  in  error  when  he  stressed  the  importance 
of  use  and  disuse  of  a  part,  or  of  modifications  due  to  environmental 
change,  in  altering  the  course  of  the  hereditary  stream,  particularly 
if  we  conceive  of  these  influences  as  being  prolonged,  possibly  over 
many  generations  ?  Have  we  not  in  the  serological  mechanism  of  the 
body  of  animals  an  adequate  means  for  the  incitement  of  the  germinal 
changes  which  underly  certain  aspects  of  evolution  ? 


CHAPTER  XXIV 

THE  MUTATION  THEORY 

[It  will  be  recalled  that  Darwin,  although  depending  upon  the 
ever-present  fluctuating  variations  as  the  material  for  natural  selection 
to  work  upon,  recognized  the  occasional  occurrence  of  ''sports"  or 
"saltatory  variations."  These,  however,  seemed  to  him  to  be  so  rare 
in  nature  as  to  offer  no  adequate  basis  for  selection.  During  the  latter 
part  of  the  nineteenth  century  several  investigators,  feeling  the 
inadequacy  of  fluctuating  variations  to  produce  qualitatively  new 
characters,  decided  to  make  a  more  careful  examination  of  animals 
and  plants  in  nature  in  order  to  discover  whether  saltatory  variations 
might  not  be  of  more  frequent  occurrence  than  Darwin  had  supposed. 

In  England  William  Bateson  collected  a  large  number  of  instances 
of  a  type  of  variation  which  he  called  discontinuous  in  contradistinc- 
tion to  the  continuous  type  which  we  have  been  calling  fluctuations. 
Such  variations,  instead  of  being  in  a  closely  graded  series  with  the 
typical  variations  of  a  species,  were  frequently  quite  sharply  different 
from  the  majority.  Although  no  experiments  were  conducted  in 
order  to  test  the  hereditability  of  these  "discontinuous  variations," 
it  is  probable  that  some  of  them  were  "mutations"  in  the  sense  of 
De  Vries. 

At  about  the  same  time  Hugo  De  Vries  in  Holland,  probably  as 
the  result  of  his  rediscovery  of  Mendel's  work  and  his  confirmation  of 
th  latter's  laws  of  heredity,  became  convinced  that  new  species  arise 
not  by  the  accumulation,  through  natural  selection,  of  minute  fluc- 
tuating variations,  but  by  the  sudden  appearance  in  one  generation 
of  fully  formed  new  elementary  species.  He  began  a  systematic 
research  for  species  of  plants  in  nature  that  were  giving  rise  to  new 
species.  Many  species  were  examined  in  their  natural  surroundings 
and  were  then  brought  into  the  experimental  garden  for  more  careful 
observation,  but  for  a  long  time  the  search  for  a  species  throwing  off 
new  elementary  species  was  unsuccessful.  Finally,  however,  in  a 
field  near  Hilversum,  in  the  vicinity  of  Amsterdam,  he  found  what 
seemed  to  him  to  be  just  the  kind  of  plant  he  had  been  looking  for  in 
the  evening,  primrose  {Oenothera  lamarckiana). 

346 


THE  MUTATION  THEORY 


347 


'Tamarck's  evening-primrose"  (Fig.  57),  says  De  Vries,  "is  a 
stately  plant,  with  a  stout  stem,  attaining  often  a  height  of  1.6  meters 
and  more.     When  not  crowded  the  main  stem  is  surrounded  by  a  large 


Fig.  57. — Oenothera  lamarckiana,  the  original  type  used  by  De\'rics  in  his 
experiments.  This  is  the  stock  from  Hilvcrsum,  from  which  arose  in  successixc 
generations  a  series  of  mutants.     {From  De  ]'ries.) 


348     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

circle  of  smaller  branches,  growing  upwards  from  its  base  so  as  to  form 
a  dense  brush The  flowers  are  large  and  bright  yellow  attract- 
ing immediate  attention  even  from  a  distance.  They  open  toward 
evening,  as  the  name  indicates,  and  are  pollinated  by  bumble-bees 
and  moths." 

On  account  of  the  classic  character  of  De  Vries's  mutants  of 
Oenothera  lamarckiana  we  shall  follow  his  own  detailed  description 
of  the  more  significant  of  these. — Ed.] 

NEW  SPECIES    (iVIUTANTS)    OF  OENOTHERA^ 
HUGO  DE  VRIES 

This  striking  species  (Oenothera  lamarckiana)  was  found  in  a 
locality  near  Hilversum,  in  the  vicinity  of  Amsterdam,  where  it  grew 
in  some  thousands  of  individuals.  Ordinarily  biennial,  it  produces 
roset.es  in  the  first,  and  stems  in  the  second  year.  Both  the  stems 
and  the  rosettes  were  at  once  seen  to  be  highly  variable,  and  soon 
distinct  varieties  could  be  distinguished  among  them. 

The  first  discovery  of  this  locality  was  made  in  1886.  Afterwards 
I  visited  it  many  times,  often  weekly  or  even  daily  during  the  first 
few  years,  and  always  at  least  once  a  year  up  to  the  present  time. 
This  stately  plant  showed  the  long-sought  pecuHarity  of  producing  a 
number  of  new  species  every  year.  Some  of  them  were  observed 
directly  on  the  field,  either  as  stems  or  as  rosettes.  The  latter  could 
be  transplanted  into  my  garden  for  further  observation,  and  the  stems 
yielded  seeds  to  be  sown  under  like  control.  Others  were  too  weak 
to  live  a  sufiiciently  long  time  in  the  field.  They  were  discovered  by 
sowing  seed  from  indifferent  plants  of  the  wild  locality  in  the 
garden.  A  third  and  last  method  of  getting  still  more  new  species 
from  the  original  strain  was  the  repetition  of  the  sowing  process,  by 
saving  and  sowing  the  seed  which  ripened  on  the  introduced  plants. 
These  various  methods  have  led  to  the  discovery  of  over  a  dozen  new 
types  never  previously  observed  or  described. 

Leaving  the  physiological  side  of  the  relations  of  these  new  forms 
for  the  next  lecture,  it  would  be  profitable  to  give  a  short  description 
of  the  several  novelties.  To  this  end  they  may  be  combined  under 
five  different  heads,  according  to  their  systematic  value.  The  first 
head  includes  those  which  are  evidently  to  be  considered  as  varieties, 

^  From  H.  De  Vries,  Species  and  Varieties  (copyright  1904).  Used  by  special 
permission  of  the  publishers,  The  Open  Court  Publishing  Company. 


THE  MUTATION  THEORY 


349 


in  the  narrower  sense  of  the  word,  as  previously  given.  The  second 
and  third  heads  indicate  the  real  progressive  elementary  species,  first 
those  which  are  as  strong  as  the  parent-species,  and  secondly  a  group 
of  weaker  types,  apparently  not  destined  to  be  successful.  Under 
the  fourth  head  I  shall  include  some  inconstant  forms,  and  under 
the  last  head  those  that  are  organically  incomplete. 

Of  varieties  with  a  negative  attribute,  or  real  retrograde  varieties, 
I  have  found  three,  all  of  them  in  a  flowering  condition  in  the  field. 
I  have  given  them  the  names  of  laevifolia,  brevistylis  and  nannella. 

The  laevifolia,  or  smooth-leaved  variety,  was  one  of  the  very  first 
deviating  types  found  in  the  original  field.  This  was  in  the  summer 
of  1887,  seventeen  years  ago.  It  formed  a  little  group  of  plants  grow- 
ing at  some  distance  from  the  main  body,  in  the  same  field.  I  found 
some  rosettes  and  some  flowering  stems  and  sowed  some  seed  in  the 
fall.  The  variety  has  been  quite  constant  in  the  field,  neither  increas- 
ing in  number  of  individual  plants  nor  changing  its  place,  though  now 
closely  surrounded  by  other  lamarckianas.  In  my  garden  it  has 
proved  to  be  constant  from  seed,  never  reverting  to  the  original 
lamarckiana,  provided  intercrossing  was  excluded. 

It  is  chiefly  distinguished  from  Lamarck's  evening-primrose  by  its 
smooth  leaves,  as  the  name  indicates.  The  leaves  of  the  original 
form  show  numerous  sinuosities  in  their  blades,  not  at  the  edge,  but 
anywhere  between  the  veins.  The  blade  shows  numbers  of  convexi- 
ties on  either  surface,  the  whole  surface  being  undulated  in  this 
manner;  it  lacks  also  the  brightness  of  the  ordinary  evening-primrose 
or  Oenothera  biennis. 

These  undulations  are  lacking  or  at  least  very  rare  on  the  leaves 
of  the  new  laevifolia.  Ordinarily  they  are  wholly  wanting,  but  at 
times  single  leaves  with  slight  manifestations  of  this  character  may 
make  their  appearance.  They  warn  us  that  the  capacity  for  such 
sinuosities  is  not  wholly  lost,  but  only  lies  dormant  in  the  new  variety. 
It  is  reduced  to  a  latent  state,  exactly  as  are  the  apparently  lost 
characters  of  so  many  ordinary  horticultural  varieties. 

Lacking  the  undulations,  the  laevifolia-leaves  are  smooth  and 
bright.  They  are  a  little  narrower  and  more  slender  than  those  of 
the  lamarckiana.  The  convexities  and  concavities  of  leaves  are  a 
useful  character  in  dry  seasons,  but  during  wet  summers,  such  as  those 
of  the  last  few  years,  they  must  be  considered  as  very  harmful,  as  they 
retain  some  of  the  water  which  falls  on  the  plants,  prolonging  the 
action  of  the  water  on  the  leaves.     This  is  considered  by  some  writers 


350     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

to  be  of  some  utility  after  slight  showers,  but  was  observed  to  be  a 
source  of  weakness  during  wet  weather  in  my  garden,  preventing  the 
leaves  from  drying.  Whether  the  laevifolia  would  do  better  under 
such  circumstances,  I  have,  however,  omitted  to  test. 

The  flowers  of  the  laevifolia  are  also  in  a  slight  degree  different 
from  those  of  lamarckiana.  The  yellow  color  is  paler  and  the  petals 
are  smoother.  Later,  in  the  fall,  on  the  weaker  side  branches  these 
differences  increase.  The  laevifolia  petals  become  smaller  and  are 
devoid  of  the  emargination  at  the  apex,  becoming  ovate  instead  of 
obcordate.  This  shape  is  often  the  most  easily  recognized  and  most 
striking  mark  of  the  variety.  In  respect  to  the  reproductive  organs, 
the  fertility  and  abundance  of  good  seed,  the  laevifolia  is  by  no  means 
inferior  or  superior  to  the  original  species. 

0.  brevistylis,  or  the  short-styled  evening-primrose,  is  the  most 
curious  of  all  my  new  forms.  It  has  very  short  styles,  which  bring 
the  stigmas  only  up  to  the  throat  of  the  calyx-tube,  instead  of  upwards 
of  the  anthers.  The  stigmas  themselves  are  of  another  shape,  more 
flattened  and  not  cylindrical.  The  pollen  falls  from  the  anthers 
abundantly  on  them,  and  germinates  in  the  ordinary  manner. 

The  ovary  which  in  lamarckiana  and  in  all  other  new  forms  is 
wholly  underneath  the  calyx-tube,  is  here  only  partially  so.  This  tube 
is  inserted  at  some  distances  under  its  summit.  The  insertion  divides 
the  ovary  into  two  parts :  an  upper  and  a  lower  one.  The  upper  part 
is  much  reduced  in  breadth  and  somewhat  attenuated,  simulating  a 
prolongation  of  the  base  of  the  style.  The  lower  part  is  also  reduced, 
but  in  another  manner.  At  the  time  of  flowering  it  is  like  the  ovary 
of  lamarckiana,  neither  smaller  nor  larger.  But  it  is  only  reached  by 
very  few  pollen- tubes,  and  is  therefore  always  very  incompletely 
fertilized.  It  does  not  fall  off  after  the  fading  away  of  the  flower,  as 
unfertilized  ovaries  usually  do;  neither  does  it  grow  out,  nor  assume 
the  upright  position  of  normal  capsules.  It  is  checked  in  its  develop- 
ment, and  at  the  time  of  ripening  it  is  nearly  of  the  same  length  as  in 
the  beginning.  Many  of  them  contain  no  good  seeds  at  all;  from 
others  I  have  succeeded  in  saving  only  a  hundred  seeds  from  thousands 
of  capsules. 

These  seeds,  if  purely  polhnated,  and  with  the  exclusion  of  the 
visits  of  insects,  reproduce  the  variety  entirely  and  without  any 
reversion  to  the  lamarckiana  type. 

Correlated  with  the  detailed  structures  is  the  form  of  the  flower- 
buds.     They  lack  the  high  stigma  placed  above  the  anthers,  which  in 


THE  MUTATION  THEORY 


351 


the  lamarcklana,  by  the  vigorous  growth  of  the  style,  extends  the  calyx 
and  renders  the  flower-bud  thinner  and  more  slender.  Those  of  the 
brevistylis  are  therefore  broader  and  more  swollen.  It  is  quite  easy 
to  distinguish  the  individuals  by  this  striking  character  alone,  although 
it  differs  from  the  parent  in  other  particulars. 

The  leaves  of  the  0.  brevistylis  are  more  rounded  at  the  tip,  but 
the  difference  is  only  pronounced  at  times,  slightly  in  the  adult 
rosettes,  but  more  clearly  on  the  growing  summits  of  the  stems  and 
branches.  By  this  character  the  plants  may  be  discerned  among  the 
others  some  weeks  before  the  flowers  begin  to  show  themselves. 

But  the  character  by  which  the  plants  may  be  most  easily  recog- 
nized from  a  distance  in  the  field  is  the  failure  of  the  fruits.  They 
were  found  nearly  every  year  in  varying,  but  always  small  numbers. 

Leaving  the  short-styled  primrose,  we  come  now  to  the  last  of 
our  group  of  retrograde  varieties.  This  is  the  0.  nannella,  or  the 
dwarf,  and  is  a  most  attractive  little  plant.  It  is  very  short  of  stature, 
reaching  often  a  height  of  only  20-30  cm.,  or  less  than  one-fourth  of 
that  of  the  parent.  It  commences  flowering  at  a  height  of  10-15  ^^^-j 
whfle  the  parent-form  often  measures  nearly  a  meter  at  this  stage  of 
its  development.  Being  so  very  dwarfed  the  large  flowers  are  all  the 
more  striking.  They  are  hardly  inferior  to  those  of  the  lamarckiana, 
and  agree  with  them  in  structure.  When  they  fade  away  the  spike 
is  rapidly  lengthened,  and  often  becomes  much  longer  than  the  lower 
or  vegetative  part  of  the  stem. 

The  dwarfs  are  one  of  the  most  common  mutations  in  my  garden, 
and  were  observed  in  the  native  locality  and  also  grown  from  seeds 
saved  there.  Once  produced  they  are  absolutely  constant.  I  have 
tried  many  thousands  of  seeds  from  various  dwarf  mutants,  and  never 
observed  any  trace  of  reversion  to  the  lamarckiana  type.  I  ha\'e  also 
cultivated  them  in  successive  generations  with  the  same  result.  In  a 
former  lecture  we  have  seen  that  contrary  to  the  general  run  of 
horticultural  belief,  varieties  are  as  constant  as  the  best  species,  if 
kept  free  from  hybrid  admixtures.  This  is  a  general  rule,  and  the  ex- 
ceptions, or  cases  of  atavism,  are  extremely  rare.  In  this  respect  it  is  of 
great  interest  to  observe  that  this  constancy  is  not  an  acquired  quality, 
but  is  to  be  considered  as  innate,  because  it  is  already  fully  developed 
at  the  very  moment  when  the  original  mutation  takes  place. 

From  its  first  leaves  to  the  rosette  period,  and  through  this  to  the 
lengthening  of  the  stem,  the  dwarfs  are  easily  distinguished  from  any 
other  of  their  congeners.     The  most  remarkable  feature  is  the  shape 


352      READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 


THE  MUTATION  THEORY  353 

of  the  leaves.  They  are  broader  and  shorter,  and  especially  at  the 
base  they  are  broadened  in  such  a  way  as  to  become  apparently 
sessile.  The  stalk  is  very  brittle,  and  any  rough  treatment  may  cause 
the  leaves  to  break  off.  The  young  seedlings  are  recognizable  by  the 
shape  of  the  first  two  or  three  leaves,  and  when  more  of  them  are 
produced,  the  rosettes  Ijecome  dense  and  strikingly  dilTerent  from 
others.  Later  leaves  are  more  nearly  like  the  parent-type,  Init  ihe 
petioles  remain  short.  The  bases  of  the  blades  are  frequently  almost 
cordate,  the  laminae  themselves  varying  from  oblong-ovate  to  ovate 
in  outline. 

The  stems  are  often  quite  unb ranched,  or  branched  only  at  the 
base  of  the  spike.  Strong  secondary  stems  are  a  striking  attribute  of 
the  lamarckiana  parent,  but  they  are  lacking,  or  almost  so  in  the 
dwarfs.  The  stem  is  straight  and  short,  and  this,  combined  with  the 
large  crown  of  bright  flowers,  makes  the  dwarfs  eminently  suitable 
for  bed  or  border  plants.  Unfortunately  they  are  very  sensitive, 
especially  to  wet  weather. 

Oenothera  gigas  and  0.  rubrinervis,  or  the  giant,  and  the  red-veined 
evening  primroses,  are  the  names  given  to  two  robust  and  stout 
species,  which  seem  to  be  equal  in  vigor  to  the  parent-plant,  while 
diverging  from  it  in  striking  characters.  Both  are  true  elementary 
species,  differentiated  from  lamarckiana  in  nearly  all  their  organs  and 
qualities,  but  not  showing  any  preponderating  character  of  a  retrograde 
nature.  Their  differences  may  be  compared  with  those  of  the  elemen- 
tary species  of  other  genera,  as  for  instance,  of  Draba,  or  of  violets, 
as  will  be  seen  by  their  description. 

The  giant  evening-primrose,  though  not  taller  in  stature  than 
0.  lamarckiana,  deserves  its  name  because  it  is  so  much  stouter  in  all 
respects.  The  stems  are  robust,  often  with  twice  the  diameter  of 
lamarckiana  throughout.  The  internodes  are  shorter,  and  the  leaves 
more  numerous,  covering  the  stems  with  a  denser  foliage.  This 
shortness  of  internodes  extends  itself  to  the  spike,  and  for  this  reason 
the  flowers  and  fruits  grow  closer  together  than  on  the  parent-plant. 
Hence  the  crown  of  bright  flowers,  opening  each  evening,  is  more  dense 
and  more  strikingly  brilliant,  so  much  the  more  so  as  the  individual 
flowers  are  markedly  larger  than  those  of  the  parents.  In  connection 
with  these  characters,  the  flower-buds  are  seen  to  be  much  stouter 
than  those  of  lamarckiana.  The  fruits  attain  only  half  the  normal 
size,  but  are  broader  and  contain  fewer,  but  larger  seeds. 


354     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

The  ruhrinervis  is  in  many  respects  a  counterpart  to  the  gigas,  but 
its  stature  is  more  slender.  The  spikes  and  flowers  are  those  of  the 
lamarckiana,  but  the  bracts  are  narrower.  Red  veins  and  red  streaks 
on  the  fruits  afford  a  striking  differentiating  mark,  though  they  are 
not  absolutely  lacking  in  the  parent-species.  A  red  hue  may  be  seen 
on  the  calyx,  and  even  the  yellow  color  of  the  petals  is  somewhat 
deepened  in  the  same  way.  Young  plants  are  often  marked  by  the 
pale  red  tinge  of  the  mid-veins,  but  in  adult  rosettes,  or  from  lack  of 
sunshine,  this  hue  is  often  very  faint. 

The  leaves  are  narrow,  and  a  curious  feature  of  this  species  is  the 
great  brittleness  of  the  leaves  and  stems,  especially  on  annual  indi- 
viduals, for  example,  on  those  that  make  their  stem  and  flowers  in 
the  first  year.  High  turgidity  and  weak  development  of  the  mechani- 
cal and  supporting  tissues  are  the  anatomical  cause  of  this  deficiency, 
the  bast-fibres  showing  thinner  walls  than  those  of  the  parent-type 
under  the  microscope.  Young  stems  of  ruhrinervis  may  be  broken 
off  by  a  sharp  stroke,  and  show  a  smooth  rupture  across  all  the  tissues, 
while  those  of  lamarckiana  are  very  tough  and  strong. 

Both  the  giant  and  the  red- veined  species  are  easily  recognized  in 
the  rosette-stage.  The  very  young  seedlings  of  the  latter  are  not 
clearly  differentiated  from  the  lamarckiana,  and  often  a  dozen  leaves 
are  required  before  the  difference  may  be  seen.  Under  ordinary 
circumstances  the  young  plants  must  reach  an  age  of  about  two 
months  before  it  is  possible  to  discern  their  characters,  or  at  least 
before  these  characters  have  become  reliable  enough  to  enable  us  to 
judge  of  each  individual  without  doubt.  But  the  divergencies  rapidly 
become  greater.  The  leaves  of  O.  gigas  are  broader,  of  a  deeper 
green,  the  blade  more  sharply  set  off  against  the  stalk,  the  whole 
rosettes  becoming  stout  and  crowded  with  leaves.  Those  of  0.  ruhri- 
nervis on  the  contrary  are  thin,  of  a  paler  green  and  with  a  silvery  white 
surface;  the  blades  are  elliptic,  often  being  only  2  cm.  or  less  in  width. 
They  are  acute  at  the  apex  and  gradually  narrowed  into  the  petiole. 

It  is  quite  evident  that  such  pale  narrow  leaves  must  produce 
smaller  quantities  of  organic  food  than  the  darker  green  and  broad 
organs  of  the  gigas.  Perhaps  this  fact  is  accountable  partly,  at  least, 
for  the  more  robust  growth  of  the  giant  in  the  second  year.  Perhaps 
also  some  relation  exists  between  this  difference  in  chemical  activity 
and  the  tendency  to  become  annual  or  biennial.  The  gigas,  as  a  rule, 
produces  far  more,  and  the  ruhrinervis  far  less  biennial  plants,  than 
the  lamarckiana.     Annual  culture  for  the  one  is  as  unreliable  as 


THE  MUTATION  THEORY  355 

biennial  culture  for  the  other.  Rubrinerms  may  be  annual  in  appar- 
ently all  specimens,  in  sunny  seasons,  which  would  allow  a  large 
part  of  the  gigas  to  remain  in  the  state  of  rosettes  during  the  entire 
first  summer.  It  would  be  very  interesting  to  obtain  a  fuller  insight 
into  the  relation  of  the  length  of  life  to  other  qualities,  but  as  yet 
the  facts  can  only  be  detailed  as  they  stand. 

Both  of  these  stout  species  have  been  found  quite  constant  from 
the  very  first  moment  of  their  appearance.  I  have  cultivated  them 
from  seed  in  large  numbers,  and  they  have  never  reverted  to  the 
lamarckiana.  From  this  they  have  inherited  the  mutability  or  the 
capacity  of  producing  in  their  turn  new  mutants.  But  they  seem  to 
have  done  so  incompletely,  changing  in  the  direction  of  more  absolute 
constancy.  This  was  especially  observed  in  the  case  of  rtibrinervis, 
which  is  not  of  such  rare  occurrence  as  O.  gigds,  and  which  it  has  been 
possible  to  study  in  large  numbers  of  individuals.  So  for  instance, 
"the  red- veins"  have  never  produced  any  dwarfs,  notwithstanding 
they  are  produced  very  often  by  the  parent-type.  And  in  crossing 
experiments  the  red-veins  gave  proof  of  the  absence  of  a  mutative 
capacity  for  their  production. 

[Besides  the  mutants  just  described  there  occurred  two  weak  forms 
that  could  survive  only  if  reared  under  protection  and  would  have 
failed  to  survive  in  nature.  Here  we  have  a  place  for  the  action  of 
natural  selection,  but  operating  with  mutations  instead  of  with 
fluctuating  variations.  These  two  mutants  are  "  the  whitish  and  the 
oblong-leaved  evening-primroses  or  the  Oenothera  albida  and  oblonga.'^ 

All  of  the  mutants  so  far  mentioned  are  constant  forms  that  breed 
true  to  type.  Certain  other  types  were  either  incapable  of  being  bred 
or  else  were  decidedly  inconstant.  Oenothera  lata  had  only  pistillate 
flowers  and  therefore  could  not  be  fertilized  by  pollen  of  the  same 
mutant.  Oenothera  scintillous  and  O.  elliptica  are  fertile  to  their  own 
pollen,  but  produce  progeny  only  partly  like  the  parent,  the  rest 
reverting  to  the  original  type  Oenothera  lamarckiana. — Ed.] 

SUMMARY   OF   DE   VRIES'S   MUTATION   THEORY' 
THOMAS    HUNT    MORGAN 

We  may  now  proceed  to  examine  the  evidence  from  which  De 
Vries  has  been  led  to  the  general  conclusions  given  in  the  preceding 
pages.     De  Vries  found  at  Hilversum,  near  Amsterdam,  a  locality 

^  T.  H.  Morgan,  Evolution  and  Adaptation  (1903).  Used  by  special  permission 
of  the  publishers,  The  Macmillan  Company. 


356     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

where  a  number  of  plants  of  the  evening  primrose,  Oenothera  lamarck- 
iana,  grow  in  large  numbers.  This  plant  is  an  American  form  that 
has  been  imported  into  Europe.  It  often  escapes  from  cultivation, 
as  is  the  case  at  Hilversum,  where  for  ten  years  it  had  been  growing 
wild.  Its  rapid  increase  in  numbers  in  the  course  of  a  few  years  may 
be  one  of  the  causes  that  has  led  to  the  appearance  of  a  mutation 
period.  The  escaped  plants  showed  fluctuating  variations  in  nearly 
all  of  their  organs.  They  also  had  produced  a  number  of  abnormal 
forms.  Some  of  the  plants  came  to  maturity  in  one  year,  others  in 
two,  or  in  rare  cases,  in  three,  years. 

A  year  after  the  first  finding  of  these  plants  De  Vries  observed  two 
well-characterized  forms,  which  he  at  once  recognized  as  new  elemen- 
tary species.  One  of  these  was  O.  brevistylis,  which  occurred  only  as 
female  plants.  The  other  new  species  was  a  smooth-leafed  form  with 
a  more  beautiful  foliage  than  O.  lamarckiana.  This  is  O.  laevifolia. 
It  was  found  that  both  of  these  new  forms  bred  true  from  self- 
fertilized  seeds.  At  first  only  a  few  specimens  were  found,  each  form 
in  a  particular  part  of  the  field,  which  looks  as  though  each  might  have 
come  from  the  seeds  of  a  single  plant. 

These  two  new  forms,  as  well  as  the  common  0.  lamarckiana,  were 
collected,  and  from  these  plants  there  have  arisen  the  three  groups  of 
famiUes  of  elementary  species  that  De  Vries  has  studied.  In  his 
garden  other  new  forms  also  arose  from  those  that  had  been  brought 
under  cultivation.  The  largest  group  and  the  most  important  one 
is  that  from  the  original  0.  lamarckiana  form.  The  accompanying 
table  shows  the  mutations  that  arose  between  1887  and  1899  from 
these  plants.  The  seeds  were  selected  in  each  case  from  self-fertilized 
plants  of  the  lamarckiana  form,  so  that  the  new  plants  appearing 
in  each  horizontal  line  are  the  descendants  in  each  generation  of 
lamarckiana  parents.  It  will  be  observed  that  the  species,  0.  oblonga, 
appeared  again  and  again  in  considerable  numbers,  and  the  same  is 
true  for  several  of  the  other  forms  also.  Only  the  two  species,  0.  gigas 
and  0.  scintillans,  appeared  very  rarely  (Fig.  59). 

Thus  De  Vries  had,  in  his  seven  generations,  about  fifty  thousand 
plants,  and  about  eight  hundred  of  these  were  mutations.  When  the 
flowers  of  the  new  forms  were  artificially  fertilized  with  pollen  from 
the  flowers  of  the  same  plant,  or  of  the  same  kind  of  plant,  they  gave 
rise  to  forms  like  themselves,  thus  showing  that  they  are  true  elemen- 
tary species.  It  is  also  a  point  of  some  interest  to  observe  that  all 
these  forms  differed  from  each  other  in  a  large  number  of  particulars. 


THE  MUTATION  THEORY 


357 


Only  one  form,  0.  scintillans,  that  appeared  eight  times,  is  not 
constant  as  are  the  other  species.  When  self-fertihzed  its  seeds 
produce  always  three  other  forms,  O.  scintillans,  0.  oblonga,  and 
O.  lamarckiana.  It  differs  in  this  respect  from  all  the  other  elementary 
species,  which  mutate  not  more  than  once  in  ten  thousand  individuals. 


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Fig.  59. — Diagram  showing  in  condensed  form  the  genealogy  of  the  Or;/<)///<T(7 
lamarckiana  family  and  its  various  mutants  during  successive  }'ears.  The  numbers 
under  each  type  represent  the  number  of  new  types  observed  each  year,     {from 

Tower.) 

From  the  seeds  of  one  of  the  new  forms,  O.  laevi folia,  collected 
in  the  field,  plants  were  reared,  some  of  which  were  0.  lamarckiana  and 
others  O.  laevifolia.  They  were  allowed  to  grow  together,  and  their 
descendants  gave  rise  to  the  same  forms  found  in  the  lamarckiana 
family,  described  above,  namely,  O.  lata,  elliptica,  nannclla,  rubri- 
nervis,  and  also  two  new  species,  0.  spatulata  and  leptocarpa. 

In  the  lata  family,  only  female  flowers  are  produced,  and,  there- 
fore, in  order  to  obtain  seeds  they  were  fertilized  with  jK^llen  from 
other  species.     Here  also  appeared  some  of  the  new  species  already 


358     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

mentioned,  namely,  alhida,  nannella,  lata,  ohlonga,  rubrinervis,  and 
also  two  new  species,  elliptica  and  subovata. 

De  Vries  also  watched  the  field  from  which  the  original  forms 
were  obtained,  and  found  there  many  of  the  new  species  that  appeared 
under  cultivation.  These  were  found,  however,  only  as  weak  young 
plants  that  rarely  flowered.  Five  of  the  new  forms  were  seen  either 
in  the  Hilversum  field,  or  else  raised  from  seeds  that  had  been  collected 
there.  These  facts  show  that  the  new  species  are  not  due  to  cultiva- 
tion, and  that  they  arise  year  after  year  from  the  seeds  of  the  parent 
form,  O.  lamarckiana. 

Conclusions. — From  the  evidence  given  in  the  preceding  pages  it 
appears  that  the  line  between  fluctuating  variations  and  mutations 
may  be  sharply  drawn.  If  we  assume  that  mutations  have  furnished 
the  material  for  the  process  of  evolution,  the  whole  problem  appears 
in  a  different  light  from  that  in  which  it  was  placed  by  Darwin  when 
he  assumed  that  the  fluctuating  variations  are  the  kind  which  give 
the  material  for  evolution. 

From  the  point  of  view  of  the  mutation  theory,  species  are  no 
longer  looked  upon  as  having  been  slowly  built  up  through  the  selec- 
tion of  individual  variations,  but  the  elementary  species,  at  least, 
appear  at  a  single  advance,  and  fully  formed.  This  need  not  neces- 
sarily mean  that  great  changes  have  suddenly  taken  place,  and  in 
this  respect  the  mutation  theory  is  in  accord  with  Darwin's  view  that 
extreme  forms  that  rarely  appear,  "sports,"  have  not  furnished  the 
material  for  the  process  of  evolution. 

As  De  Vries  has  pointed  out,  each  mutation  may  be  different  from 
the  parent  form  in  only  a  slight  degree  for  each  point,  although  all 
the  points  may  be  different.  The  most  unique  feature  of  these  muta- 
tions is  the  constancy  with  which  the  new  form  is  inherited.  It  is 
this  fact,  not  previously  fully  appreciated,  that  De  Vries's  work  has 
brought  prominently  into  the  foreground.  There  is  another  point  of 
great  interest  in  this  connection.  Many  of  the  groups  that  Darwin 
recognized  as  varieties  correspond  to  the  elementary  species  of  De 
Vries.  These  varieties,  Darwin  thought,  are  the  first  stages  in  the 
formations  of  species,  and,  in  fact,  cannot  be  separated  from  species 
in  most  cases.  The  main  difference  between  the  selection  theory  and 
the  mutation  theory  is  that  the  one  supposes  these  varieties  to  arise 
through  selection  of  individual  variations,  the  other  supposes  that 
they  have  arisen  spontaneously  and  at  once  from  the  original  form. 
The  development  of  these  varieties  into  new  species  is  again  sup- 
posed, on  the  Darwinian  theory,  to  be  the  result  of  further  selection, 


THE  MUTATION  THEORY 


359 


on  the  mutation  theory,  the  result  of  the  appearance  of  new  muta- 
tions. 

In  consequence  of  this  difference  in  the  two  theories,  it  will  not 
be  difficult  to  show  that  the  mutation  theory  escapes  some  of  the 
gravest  difficulties  that  the  Darwinian  theory  has  encountered. 
Some  of  the  advantages  of  the  mutation  theory  may  be  briefly 
mentioned  here. 

1.  Since  the  mutations  appear  fully  formed  from  the  beginning, 
there  is  no  difficulty  in  accounting  for  the  incipient  stages  in  the 
development  of  an  organ,  and  since  the  organ  may  persist,  even  when 
it  has  no  value  to  the  race,  it  may  become  further  developed  by  later 
mutations  and  may  come  to  have  finally  an  important  relation  to  the 
life  of  the  individual. 

2.  The  new  mutations  may  appear  in  large  numbers,  and  of  the 
different  kinds  those  will  persist  that  can  get  a  foothold.  On  account 
of  the  large  number  of  times  that  the  same  mutations  appear,  the 
danger  of  becoming  swamped  through  crossing  with  the  original  form 
will  be  lessened  in  proportion  to  the  number  of  new  individuals  that 
arise. 

3.  If  the  time  of  reaching  maturity  in  the  new  form  is  different 
from  that  in  the  parent  forms,  then  the  new  species  will  be  kept  from 
crossing  with  the  parent  form,  and  since  this  new  character  will  be 
present  from  the  beginning,  the  new  form  will  have  much  better 
chances  of  surviving  than  if  a  difference  in  time  of  reaching  maturity 
had  to  be  gradually  acquired. 

4.  The  new  species  that  appear  may  be  in  some  cases  already 
adapted  to  live  in  a  different  environment  from  that  occupied  by  the 
parent  form;  and  if  so,  it  will  be  isolated  from  the  beginning,  which 
will  be  an  advantage  in  avoiding  the  bad  effects  of  intercrossing. 

5.  It  is  well  known  that  the  differences  between  related  species 
consist  largely  in  differences  of  unimportant  organs,  and  this  is  in 
harmony  with  the  mutation  theory,  but  one  of  the  real  difficulties  of 
the  selection  theory. 

6.  Useless  or  even  slightly  injurious  characters  may  appear  as 
mutations,  and  if  they  do  not  seriously  affect  the  perpetuation  of  the 
race,  they  may  persist. 

CRITICISMS 

[Oenothera  lamarckiana  has  fallen  under  suspicion  of  being  of 
impure  stock  due  to  the  crossing  of  two  or  more  original  species.     The 


360     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

basis  for  this  suspicion  is  that  the  type  found  in  Holland  is  not  a  truly 
wild  indigenous  species,  but  a  domestic  type  escaped  from  cultivation. 
It  seems  probable  that  the  species  was  imported  from  America  a  great 
many  years  ago.  B.  M.  Davis  has  succeeded  in  producing  by  cross- 
ing two  American  wild  species  a  hybrid  form  distinctly  resembling 
Oenothera  lamarckiana  in  numerous  respects,  and  this  hybrid,  like  any 
other  hybrid,  produces  numerous  combinations  of  the  parental  charac- 
ters when  inbred,  and  these  hybrid  progeny  sometimes  resemble  the 
mutants  observed  by  De  Vries.  It  is  also  said  that  the  pollen  grains 
of  Oenothera  lamarckiana  exhibit  a  high  degree  of  sterility,  which  is 
a  characteristic  defect  of  hybrid  plants. 

Whether  or  not,  however,  the  Oenothera  situation  be  taken  as 
valid  evidence  of  the  occurrence  of  mutations,  the  idea  of  mutations 
and  their  role  in  evolution  will  stand  up  on  quite  independent  grounds. 
Numerous  mutations  have  been  observed  in  all  sorts  of  animals  and 
plants.  Professor  T.  H.  Morgan  and  his  able  corps  of  collaborators 
have  observed  in  their  carefully  controlled  breeding  experiments  with 
the  fruit  fly  Drosophila  melanogaster  hundreds  of  suddenly  appearing 
new  characters  which  are  classed  by  them  as  mutants,  and  whose 
heredity  has  been  most  accurately  studied.  These  mutants  involve 
single  characters  of  the  organism  which  are  sometimes  of  a  prominent 
and  readily  recognizable  sort  and  sometimes  of  so  slight  a  degree  as 
to  be  imperceptible  except  to  the  trained  eye  of  the  expert  student  of 
genetics.  It  also  frequently  occurs  that  two  mutants  are  to  the  eye 
practically  identical,  but  may  be  distinguished  by  differences  in 
hereditary  behavior.  The  great  majority  of  the  mutants  discovered 
in  Drosophila  are  termed  "lethals"  because  they  involve  the  death 
of  the  mutants  possessing  the  variation.  A  further  discussion  of 
Drosophila  "mutants"  appears  in  a  later  chapter. — Ed.] 

CAUSES    OF   MUTATIONS 

[Various  mutations  have  been  produced  experimentally  by  subject- 
ing the  germ  cells  to  radically  changed  environmental  conditions. 
W.  L.  Tower  claims  to  have  produced  at  least  two  new  elementary 
species  of  potato  beetle  by  subjecting  the  already  grown  and  unchange- 
able parents  to  radically  changed  temperature  and  humidity  conditions. 
Although  the  parents  could  undergo  no  change  themselves  they 
produced  a  small  number  of  offspring  with  distinctly  changed  charac- 
ters.    These  turned  out  to  be  mutants  because  they  bred  true  to  the 


THE  MUTATION  THEORY 


361 


new  characters.     Three  of  Tower's   mutants  of   the  potato  beetle 
(Leptinotarsa  decemliueata)  are  shown  in  I-'iirure  60. 

MacDougal  injected  into  the  ovules  of  various  species  of  plants 
such  foreign  materials  as  solutions  of  zinc  salts,  cane  sugar,  etc.  The 
seeds  produced  from  these  plants  developed  into  plants  with  radicallv 


Fig.  60. — Some  divergent  types  (mutations)  of  beetles  produced  by  subject- 
ing the  germ  cells  to  external  influences.  A,  normal  dcccmlincata;  B,  the  form 
pallida;  C,  tortuosa;  D,  dcfecio punctata.     {From  Tinccr.) 

new  characters  (Fig.  61)  which  bred  true  to  type  for  four  or  more 
generations.  Whether  or  not  the  changes  persisted  longer  we  do  not 
know,  since  MacDougal  has  not  published  any  further  details. 

Gager  discovered  that  the  action  of  radium  rays  on  the  pollen 
grains  of  various  plants  had  a  profound  etTect  uix)n  the  chromatin. 
Some  of  the  latter  was  apparently  lost  during  mitotic  cell  division. 
The  same  writer  exposed  the  ovules  of  plants  to  radium  rays  and  |-)ro- 
duced  marked  changes  in  the  germ  cells  so  that  they  grew  into  various 


362     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

stunted  and  otherwise  abnormal  plants,  some  of  which  bred  true  for 
several  generations.  The  work  was  not  followed  long  enough  to 
determine  whether  the  change  was  one  involving  a  rather  prolonged 
induction  or  was  a  permanent  mutation. — Ed.] 


y^LjpJjSs' 

-rirBMB 

w 

v3j 

lifc 

B 

Fig.  61. — Two  plants  of  Onagra  biennis,  showing  the  effect  of  injections  of 
zinc  sulphate  into  the  ovule.  A,  normal;  B,  the  modified  plant,  which  arose  from 
seeds  that  had  been  modified  by  zinc  sulphate.     {From  MacDongal.) 


THE  MUTATION  THEORY  363 


Baur's  third  category  of  variations,"  say  Babcock  and  Clausen,' 
comprises  all  inheritable  changes  due  to  causes  other  than  segregation 
and  recombination  of  genetic  factors.  Although  comparatively  little 
is  known  concerning  the  specific  causes  of  mutations,  yet  it  is  possible 
to  distinguish  between  two  general  classes  of  such  inheritable  varia- 
tions according  to  the  nature  of  the  genetic  units  involved.  These 
classes  are  (i)  alterations  in  genetic  factors,  and  (2)  deviations  in  the 
number  of  chromosomes.  We  designate  the  first  group  as  factor 
mutations  and  the  second  as  chromosome  aberrations.  Since  the 
first  group  is  of  vastly  greater  importance  to  agriculture  than  the 
second,  we  shall  consider  the  latter  very  briefly  before  engaging  in 
discussion  of  the  former,  which  we  deem  worthy  of  recognition  as 
mutations  in  the  strict  sense. 

"Chromosome  aberrations. — By  the  aid  of  cytology  it  has  been 
demonstrated  that  inheritable  changes  are  occasionally  induced,  in 
plants  at  least,  by  irregularities  in  the  behavior  of  the  chromosomes 
during  mitosis  or  meiosis,  such  that  certain  germ  cells  contain  fewer 
or  more  chromosomes  than  the  number  typical  of  the  species.  Aber- 
rant forms  in  several  plant  families  are  now  known  to  differ  from  the 
parent  species  in  chromosome  number.  Some  have  only  a  single 
chromosome  more  or  less  than  the  parent,  while  a  few  are  known  in 
which  the  original  number  is  doubled.  It  is  possible  that  aberrations 
occur  involving  all  combinations  of  numbers  between  these  two 
extremes.  In  various  forms  of  Lamarck's  evening  primrose  {Oowthcra 
lamarckiana) ,  whose  typical  number  is  14,  according  to  Gates  the 
following  aberrant  numbers  have  been  reported — 15,  20,  21,  22,  2^, 
27,  28,  29,  30.  Aberrations  involving  the  doubling  of  the  number  of 
chromosomes  typical  of  the  species  is  known  as  tetraploidy  because 
there  are  four  times  the  haploid  number  typical  of  the  parent.  Oc- 
casionally aberrations  or  hybridization  between  diploid  and  tetraploid 
forms  result  in  triploidy. 

''There  is  a  limited  amount  of  evidence  which  indicates  that 
groups  of  species  have  arisen  by  progressive  alterations  in  chromosome 
number.  Thus  in  Drosophila,  Metz  has  found  ten  species  in  which 
the  chromosome  numbers  range  from  6  to  12  and  the  larger  numbers 
appear  to  have  arisen  by  subdivision  of  the  large  dumbbell-shaped 
chromosomes  found  in  the  species  having  smaller  numbers.  Evidence 
that  doubling  of  the  chromosome  number  may  occur  during  somato- 
genesis  has  been  found  by  Farmer  and  Digby  in  the  interesting  hybrid 

»  From  E.  B.  Babcock  and  R.  E.  Clausen,  Genetics  in  Relation  to  Agriculture 
(copyright  19 18).  Used  by  special  permission  of  the  publishers,  The  McGraw- 
Hill  Book  Company. 


364     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

Primula  kewensis.  The  original  plant,  which  was  sterile,  'had  18 
and  9  chromosomes  in  its  premeiotic  and  postmeiotic  nuclei  respec- 
tively,' but  in  the  fertile  plants  which  were  propagated  asexually 
from  it,  as  well  as  in  similar  fertile  hybrids  which  were  produced  in 
later  experiments,  the  diploid  and  haploid  numbers  were  36  and  18 
respectively.  Having  found  by  means  of  careful  measurements  of  the 
chromosomes  in  the  two  forms  that  the  nuclei  in  both  forms  contain 
the  same  volume  of  chromatin,  the  authors  conclude  that  the  increase 
in  number  may  be  attributed  to  transverse  fission  of  the  18  larger 
chromosomes  and  not  to  the  fusion  of  two  nuclei. 

''From  a  study  of  chromosomal  dimensions  in  relation  to  phylo- 
geny.  Meek  'arrived  at  the  conclusion  that  the  widths  of  chromosomes 
are  successively  greater  in  higher  zoological  phyla,  and  that  this 
dimension  is  constant  for  very  large  groups  of  animals.'  But  Farmer 
and  Digby  have  shown  that  such  a  conclusion  is  without  foundation 
since  'closely  related  forms  may  possess  chromosomes  differing  widely 
in  shape  and  size  and  character.'  Hence  they  conclude  'that  phylo- 
genetic  affinity  is  not,  necessarily,  correlated  with  chromosome  width.' 
They  also  point  out  that  'unfortunately  we  know  practically  nothing 
about  the  phylogeny  of  the  chromosomes.  No  convincing  hypothesis 
has  been  put  forward  to  explain  how  these  remarkable  bodies  have 
become  organized,  nor  how  their  peculiarities  have  either  been  brought 
into  existence  or  are  kept  so  true  for  a  given  species.'  However,  we 
are  reminded  by  Glaser  that  chromatin  is  present  in  bacteria  though 
not  in  the  form  of  a  nucleus  and  it  may  not  be  too  much  to  hope  that 
cytology  may  yet  discover  the  principal  stages  in  the  development  of 
the  chromosomes  and  establish  such  correlation  as  may  exist  between 
this  development  and  organic  evolution.  Certainly  extended  investi- 
gations of  chromosome  numbers  must  be  made  before  chromosome 
aberrations  can  be  considered  an  important  factor  in  evolution. 
Except  that  certain  chromosome  aberrations,  such  a  tetraploidy 
causing  gigantism,  might  be  of  economic  value,  in  general  this  class 
of  mutations  is  of  minor  importance  in  breeding." 

[Conclusion. — In  bringing  this  discussion  of  the  causes  of  heritable 
variations  (mutations)  to  a  close,  we  find  ourselves  in  a  somewhat 
pessimistic  frame  of  mind.  When  all  is  said,  it  is  found  that  our 
knowledge  of  what  actually  causes  mutations  is  almost  nothing.  We 
think  we  know  something  about  the  mechanism  of  heredity,  but  we 
do  not  know  the  mechanism  of  variation.  The  really  great  evolution- 
ary discovery  of  the  future  will  probably  be  the  finding  out  of  the 
cause  or  the  causes  of  mutations. — Ed.] 


CHAPTER  XXV 

BIOMETRY   (THE    STATISTICAL    STUDY    OF    VARIATION 

AND    HEREDITY) 

THE  STATISTICAL  STUDY  OF  VARIATION 

H.  H.  Newman 

The  pioneer  workers  in  the  appHcation  of  statistical  methods  to 
biological  study  were  Sir  Francis  Galton  and  his  leading  disciple,  Karl 
Pearson.  The  use  to  which  Galton  and  Pearson  put  their  statistical 
methods  appears  later  in  this  chapter.  For  present  purposes  we  may 
limit  our  study  of  biometry  to  that  part  of  it  which  has  to  do  with 
variation.  We  have  already  discussed  fluctuating  variations,  the 
small  plus  and  minus  differences  that  exist  between  the  different  mem- 
bers of  the  same  species  or  variety.  This  was  the  type  of  variation 
that  Darwin  considered  the  main  raw  material  of  evolution.  Exam- 
ples of  fluctuating  variations  are  not  far  to  seek.  Pearson  cites  as  an 
illustration  of  fluctuating  variation  the  number  of  veins  in  two  sets  of 
beech  leaves,  each  set  from  a  different  tree: 


Number  of  veins 

13 

14 

15 

16 

17 

18 

19 

20 

N^umber  of  leaves 

First  tree  

I 
9 

4 

8 

7 
2 

9 

4 

I 

26 

Second  tree 

3 
3 

4 

26 

9 

Total 

4 

10 

12 

9 

4 

I 

It  will  be  noted  that  though  there  were  i6-veined  leaves  on  both 
trees,  as  weU  as  15-  and  17-veined,  the  general  distribution  is  quite 
different  in  the  two  trees.  In  the  first  tree  the  most  frequently  occur- 
ring type  is  the  19-veined  leaf,  and  the  other  types  may  be  said  to 
fluctuate  about  this  (the  ''mode")-  In  the  second  tree  the  mode  is 
the  15-veined  type  and  the  other  types  fluctuate  about  it.  It  will  be 
seen  also  at  a  glance  that  the  types  that  differ  most  from  the  mode  are 
the  least  frequent  and  that  those  nearest  the  mode  are  the  most  fre- 
quent. 

Some  years  ago  the  writer  had  occasion  to  study  the  heredity  of 
scale  numbers  in  the  banded  region  of  the  nine-banded  armadillo. 
As  a  preliminary  to  this  study  it  was  necessary  to  know  the  degree  and 

365 


366     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

extent  of  variability  present  in  the  species.  Consequently  508  indi- 
viduals were  taken  at  random  and  their  scale  or  scute  number  counted. 
It  was  found  that  the  total  number  of  scutes  in  the  nine  bands  ranged 
from  517  to  625  and  that  the  commonest  number  was  about  557.  In 
order  to  get  a  definite  idea  of  the  distribution  of  the  different  types, 


in 
1 

CM 

ro 

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■<»■ 

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1 

CO 

in 

in 

in 

in 

CM 

IP 
1 

0 

CO 

in 
f 

in 

CM 

in 

in 

in 

C^ 
in 

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in 

in 

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in 

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00     lO  ^  CM  c>  tn 

CO       CTl  O  •-  CM  cs 

in     in  ID  '^  IX)  lo' 

i      '  '  I      I  I 

0>  r^  in  fr)  .— 

00  CTl  O  .-  CM 

in  m  lo  ^  ID 


00 
in 


Fig.  62. — Polygon  of  variation  for  the  total  number  of  scutes  in  the  nine 
bands  of  the  armadillo  (Dasypus  novemcinctus) ,  as  determined  by  the  seriation  of 
508  individuals.  Class  range  =  8  scutes.  The  solid  line  represents  the  observa- 
tional, and  the  broken  line  the  theoretical,  normal  curve.  The  abscissae  refer  to 
the  number  of  scutes,  and  the  ordinates  to  the  number  of  individuals.  {From 
Newman.) 

they  were  arranged  in  a  variation  polygon  as  shown  in  Figure  62.  On 
the  abscissa  are  arranged  groups  including  individuals  between  517 
and  524  scutes  inclusive,  those  between  525  and  532,  those  between 
533  and  540,  on  up  to  a  group  of  those  from  621  to  625.  All  of  these 
except  the  last  included  a  small  class  with  a  range  of  8  scutes.  This 
arranging  in  classes  was  essential,  for  without  it  there  would  have  been 


BIOMETRY  367 

113  classes  and  a  very  irregular  and  meaningless  distribution.  On  the 
ordinate  we  find  by  tens  the  numbers  of  individuals  in  each  class.  It 
will  be  noted  that  the  solid  line  is  one  connecting  the  points  of  inter- 
section between  the  class  of  scute  numl)ers  and  the  numljcr  of  indi- 
viduals in  these  classes.  The  dotted  line  represents  an  ideal  fluctuat- 
ing variation  curve,  which  is  practically  a  mathematical  curve  of 
chance.  The  closeness  of  fit  between  the  actual  and  the  theoretical 
curve  is  very  good.  The  mode  is  the  class  including  individuals  with 
a  scute  count  of  557-64,  and  there  is  a  fairly  even  balance  of  individuals 
in  the  plus  and  the  minus  directions.  It  seems  fairly  evident  from 
examination  of  the  curve  that  the  individuals  with  613  scutes  and 
over  are  beyond  the  limits  of  the  theoretical  distril)ution.  A  further 
study  of  these  exceptional  individuals  shows  that  they  are  mutations, 
in  which  a  splitting  up  of  single  scutes  into  paired  and  twinned  scutes 
has  taken  place  to  such  an  extent  as  greatly  to  increase  the  total  num- 
ber of  scutes. 

From  the  data  used  in  constructing  this  variation  polygon  several 
significant  constants  may  be  obtained.  The  ''arithmetical  mean" 
(average  number  of  scutes  in  the  entire  508  individuals)  is  558.2. 
The  ''median"  or  halfway  point  between  the  extremes  is  558.  The 
"mode"  or  most  frequently  occurring  single  type  is  557  (the  theoreti- 
cal value  being  557.6). 

If  we  wished  to  compare  a  large  group  of  parents  with  a  large  group 
of  offspring,  or  if  it  were  necessary  to  compare  the  armadillos  of  Texas 
with  those  of  Mexico  or  Brazil,  we  could  compare  them  as  to  mean, 
median,  and  mode,  and  also  as  to  the  shape  of  the  polygon  of  variation. 
This  would  give  us  a  very  good  idea  as  to  whether  or  not  the  old  species 
present  in  these  three  regions  is  tending  to  evolve  in  ditlerent  directions 
under  different  conditions  of  life. 

Instead  of  having  to  depend  on  the  visual  comparison  between  the 
variation  polygon  of  two  or  more  different  populations,  we  can  reduce 
the  facts  about  the  distribution  of  the  different  types  about  the  mean 
or  mode  to  a  simple  arithmetical  constant,  called  the  ''standard 
deviation,"  which  is  usually  given  the  symbol  a.  This  constant  is 
computed  as  follows:  

In  this  formula  x  represents  the  deviation  of  each  class  from  the 
arithmetical  mean;  /,  the  number  of  individuals  in  each  separate  class; 
S,  the  sum  of  all  the  classes,  and  ;/,  the  total  number  of  individuals. 


368     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

By  the  use  of  this  formula  we  have  calculated  the  standard  devia- 
tion ((j)  of  the  individuals  represented  in  Figure  62  to  be  14.89  =±= 
0.31  scutes.  This  means  that  the  average  deviation  from  the  mean 
is  about  14.89  scutes. 

The  =*=o.3i  scutes  is  called  the  "probable  error"  and  means  that 
the  figure  14.89  is  inaccurate  to  the  extent  of  being  0.31  scutes  too 
high  or  too  low.  The  probable  error  is  an  essential  feature  of  such 
computations,  as,  without  it,  we  would  not  be  able  to  rely  on  the  signifi- 
cance of  small  differences.  Suppose,  for  example,  we  should  find  that 
the  armadillos  of  Brazil  had  a  standard  deviation  of  15.43  ±0.44  scutes, 
we  might  conclude  that  the  variability  of  the  Brazilian  individuals  was 
0.34  scutes  greater  than  that  of  the  Texas  individuals.  In  view  of  the 
fact,  however,  that  the  probable  error  in  one  case  is  ±0.31  scutes  and 
in  the  other  ±0.44  scutes  we  would  have  to  conclude  that  there  was  no 
significant  difference.  In  actual  practice  it  has  been  decided  that 
unless  the  actual  difference  between  two  constants  is  about  4.6  times 
as  great  as  the  probable  error,  the  difference  is  not  significant. 

The  method  of  determining  the  probable  error  of  any  calculated 

constant  is  difficult  to  understand,  but  easy  to  put  into  practice.     For 

example,  the  formula  for  calculating  the  probable  error  of  the  standard 

deviation  is  as  follows: 

0.67450- 


E(T  = 


V  271 


where  E  is  the  probable  error,  and  n  the  number  of  individuals.  It 
will  be  seen  that  the  probability  of  error  diminishes  steadily  with  the 
increase  in  number  of  individuals  studied.  With  very  large  numbers 
the  error  due  to  what  is  known  as  ''random  sampling"  practically 
disappears. 

BIMODAL  AND  MULTIMODAL  CURVES 

If  we  confine  our  biometrical  studies  to  homogeneous  populations, 
we  get  only  fairly  simple  monomodal  curves  that  resemble  the  normal 
curve  of  variation,  which  is  a  curve  of  chance;  but  when  we  study 
ordinary  wild  populations,  we  frequently  find  that  we  are  dealing  with 
a  complex  of  several  races,  each  of  which  has  its  own  mode  and  stand- 
ard deviation.  Bateson  has  given  us  a  classic  example  of  this  type 
of  phenomenon.  In  studying  the  length  of  pinchers  in  the  common 
earwig  {Forjiculata  auricularia) ,  he  found  that  he  got  a  two-humped 
or  bimodal  curve  as  shown  in  Figure  63.  It  then  became  evident  that 
there  were  two  distinct  varieties  as  figured  above.  Such  studies  have 
frequently  revealed  the  heterogeneity  of   supposedly  homogeneous 


BIOMETRY 


369 


populations.  Opinion  differs  as  to  the  significance  of  these  Inuiings. 
The  more  optimistic  evolutionists  look  upon  such  instances  as  that  of 
Bateson's  earwigs  as  visual  demonstrations  of  a  species  actually  split- 
ting up  into  two  or  more  species.  It  seems  quite  Hkely  that  one  of 
these  types  is  a  successful  mutant  type  that  has  not  fully  segregated 
itself  as  a  true  species  from  the  parent-type.  Another  view  of  the 
significance  of  bimodal  curves  is  that  the  condition  results  from  hybridi- 
zation and  that  the  bimodality  is  the  result  of  the  segregation  of 
dominant  and  recessive  types. 


A 

/ 

\ 

r~ 

T 

\ 

/ 

\ 
\ 

/ 

\ 

\^^ 

^ 

\ 
\ 

^T-n- 

3  4  5  6  7  8  9 

Fig.  63. — Bimodal  polygon  plotted  from  data  on  the  earwig.  Mean  types 
(X|)  indicated  above  corresponding  modes.  Numbers  below  the  base  line  indicate 
length  of  pincers  in  millimeters.     {From  Bateson  and  Johannscn.) 


THE  COEFFICIENT  OF  CORRELATION 

Only  one  more  biometrical  constant  need  be  mentioned  here:  the 
''coefficient  of  correlation."  It  is  often  necessary  to  discover  the 
exact  relation  that  exists  between  two  sets  of  variables  in  order  to 
discover  whether  they  are  totally  independent  or  partially  correlated 
with  each  other.  For  example,  we  have  found  that  there  is  a  close 
correlation  between  stature  and  head  length  in  man,  also  between 
color  of  hair  and  color  of  eyes;  but  it  is  very  important  to  be  able  to 
reduce  the  degree  of  correlation  to  a  simple  arithmetical  constant. 
This  is  called  the  "coefficient  of  correlation"  (commonly  expressed 
as  Yxy,  where  x  is  one  variable  and  y  the  other).  The  formula  for  com- 
puting r^y  is  as  follows: 


^xy 


n 


\^3f^y 


370     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

where  d  represents  the  actual  deviation  and  2  the  sum,  n  the  number 
of  individuals;  a  the  standard  deviation. 

"Correlation  tables"  show  graphically  whether  or  not  there  is 
correlation.  If,  as  in  Figure  64,  we  want  to  find  out  what  is  the  rela- 
tionship between  total  yield  of  oats  and  number  of  culms  to  the  plant, 
we  may  make  a  table  with  subject  classes  arranged  perpendicularly, 
and  the  relative  classes,  horizontally.  If  the  individuals  tend  to  group 
themselves  about  a  diagonal  ranging  from  upper  left-  to  lower  right- 
hand  corners,  the  amount  of  correlation  is  quite  marked.  Complete 
correlation  would  be  represented  by  a  single  line  of  points  along  this 
diagonal.     No  correlation  would  be  shown  by  random  distributing 

2  3  4  5  6        7 


0-1 

3 

3 

1-2 

28 

19 

3 

50 

2-3 

18 

66 

20 

1 

1 

106 

3-4 

1 

42 

58 

7 

1 

109 

4-5 

7 

59 

11 

3 

80 

5-6 

26 

14 

2 

42 

&-7 

4 

3 

7 

7-8 

1 

1 

2 

8-9 

1 

1 

50 


134 


167 


38 


10 


1       400 


Fig.  64. — Correlation  table  of  400  plants  of  Sixty-Day  oats.  Total  yield  of 
plant  in  grams,  subject.  Number  of  culms  per  plant,  relative.  19 10.  Coefficient 
of  correlation  =  o. 712 ±0.017.     {From  Love  and  Leighty,  1914.) 

over  the  whole  rectangle.  Inverse  correlation  would  tend  to  give  a 
grouping  about  a  diagonal  ranging  from  the  upper  right-  to  lower 
left-hand  corners. 

In  the  particular  correlation  table  used  for  illustration,  the  coeffi- 
cient of  correlation  (vxy)  turns  out  to  be  0.712^0.017.  Since  com- 
plete correlation  would  be  i,  the  degree  of  positive  correlation  is  very 
high,  as  we  might  expect.  The  correlation  table  was  used  quite 
effectively  by  Galton,  as  we  shall  now  show. 


STATISTICAL   STUDY   OF   INHERITANCE^ 
EDWIN   GRANT  CONKLIN 

Francis  Galton  was  one  of  the  first  who  attempted  to  reduce  the 
mass  of  conflicting  observations  on  heredity  and  variation  to  some 

*From  E.  G.  Conklin,  Heredity  and  Environment   (copyright  1920).    Used  by 
special  permission  of  the  publishers,  The  Princeton  University  Press. 


BIOMETRY 


371 


system  and  to  establish  certain  principles  as  a  result  of  statistical 
study.  He  was  the  real  founder  of  the  scientific  study  of  inheritance; 
he  studied  characters  singly  and  he  introduced  quantitative  measures. 
Galton's  researches,  which  were  i)ublished  in  several  volumes,  con- 
sisted chiefly  in  a  study  of  certain  families  with  regard  to  several 
selected  traits,  viz.,  genius  or  marked  intellectual  capacity,  artistic 
faculty,  stature,  eye  color  and  disease.  As  a  result  of  his  very  e.xten- 
sive  studies  two  main  principles  appeared  to  be  established : 

I.  The  Law  of  Ancestral  Inheritance  which  he  stated  as  follows: 
The  two  parents  contribute  between  them  on  the  average  one-half 
of  each  inherited  faculty,  each  of  them  contributing  one-quarter  of 
it.  The  four  grandparents  contribute  between  them  one-quarter,  or 
each  of  them  one-sixteenth ;  and  so  on,  thesum  of  the  series  I  +  4  +  s  +  iV, 
being  equal  to  i,  as  it  should  be.  It  is  a  property  of  this  infinite  series 
that  each  term  is  equal  to  the  sum  of  all  those  that  follow:    thus 

i  =  |+|+iV  .  .  .  .  ,  4  =  l+iV+  •  •  .  .  ,  and  so  on.  The  pre- 
potencies of  particular  ancestors  in  any  given  pedigree  are  eliminated 
by  a  law  which  deals  only  with  average  contributions,  and  the  various 
prepotencies  of  sex  with  respect  to  different  qualities  are  also  presum- 
ably eliminated. 

The  average  contribution  of  each  ancestor  was  thus  stated  defi- 
nitely, the  contribution  diminishing  with  the  remoteness  of  the  ances- 
tor. This  Law  of  Ancestral  Inheritance  is  represented  graphically  in 
Figure  65.  Pearson  has  somewhat  modified  the  figures  given  by 
Galton,  holding  that  in  horses  and  dogs  the  parents  contribute  ^,  the 
grandparents  J,  the  great-grandparents  |,  etc. 

Number  of  ancestors. — Theoretically  the  number  of  ancestors 
doubles  in  each  ascending  generation;  there  are  two  parents,  four 
grandparents,  eight  great  grandparents,  etc.  If  this  continued  to  be 
true  indefinitely  the  number  of  ancestors  in  any  ascending  generation 
would  be  (2)",  in  which  n  represents  the  number  of  generations. 
There  have  been  about  57  generations  since  the  beginning  of  the  Chris- 
tian Era,  and  if  this  rule  held  true  indefinitely  each  of  us  would  have 
had  at  the  time  of  the  birth  of  Christ  a  number  of  ancestors  repre- 
sented by  (2)"  or  about  120  quadrillions — a  number  far  greater  than 
the  entire  human  population  of  the  globe  since  that  time.  As  a 
matter  of  fact,  owing  to  the  intermarriage  of  cousins  of  various  degrees, 
the  actual  number  of  ancestors  is  much  smaller  than  the  theoretical 
number.  For  example,  Plate  says  that  the  late  Emperor  of  Germany 
had  only  162  ancestors  in  the  loth  ascending  generation,  instead  of 


372     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

512,  the  theoretical  number.  Nevertheless  this  calculation  will  serve 
to  show  how  widespread  our  ancestral  lines  are,  and  how  nearly  related 
are  all  people  of  the  same  race. 

Davenport  concludes  that  no  people  of  Enghsh  descent  are  more 
distantly  related  than  30th  cousins,  while  most  people  are  much  more 
closely  related  than  that.  If  we  allow  three  generations  to  a  century, 
and  calculate  that  the  degree  of  cousinship  is  determined  by  the  num- 
ber of  generations  less  two,  since  first  cousins  appear  only  in  the  third 
generation,  the  first  being  that  of  the  parents  and  the  second  that  of 
the  sons  and  daughters,  we  find  that  30th  cousins  at  the  present  time 


d' 

9 

cT 

? 

S 

? 

cT 

? 

c5' 

? 

d 

? 

<S 

? 

c^ 

$ 

6 

9 

S 

$ 

6 

? 

6 

? 

S 

9 

S 

9 

J 

9 

1  1 

1  1 

1  1 

1  1 

1  1 

1  1 

1  I 

1  1 

1  1 

1  1 

1  1 

1  1 

1  1 

1  1 

1  1 

1  1 

Parents 


Grand  Pts 


Gt  Gd  Pts 


Gt  g\  Gd  P\s 


Fig.  65. — Diagram  of  Galton's  "Law  of  Ancestral  Inheritance."  The  whole 
heritage  is  represented  by  the  entire  rectangle;  that  derived  from  each  progenitor 
by  the  smaller  squares;  the  number  of  the  latter  doubles  in  each  ascending 
generation  while  its  area  is  halved.     {From  Conklin,  after  Thomson.) 


would  have  had  a  common  ancestor  about  one  thousand  years  ago  or 
approximately  at  the  time  of  William  the  Conqueror.  As  a  matter  of 
fact  most  persons  of  the  same  race  are  much  more  closely  related  than 
this,  and  certainly  we  need  not  go  back  to  Adam  nor  even  to  Shem, 
Ham,  or  Japheth  to  find  our  common  ancestor. 

2.  The  Law  of  Filial  Regression  is  the  second  principle  which 
Galton  deduced  from  his  statistical  studies,  or  it  may  be  called  the 
tendency  to  mediocrity.  He  found  that,  on  the  average,  extreme 
peculiarities  of  parents  were  less  extreme  in  children.  Thus  "the 
stature  of  adult  offspring  must  on  the  whole  be  more  mediocre  than 
the  stature  of  their  parents,  that  is  to  say  more  near  to  the  mean  or 
mid  of  the  general  population";  and  again,  "the  more  bountifully  a 


BIOMETRY 


373 


parent  is  gifted  by  nature,  the  more  rare  will  be  his  good  fortune  if  he 
begets  a  son  who  is  as  richly  enrlowed  as  himself. "  This  so-called  law 
of  filial  regression  is  represented  graphically  in  Figure  66  in  which  the 
actual  stature  of  individual  parents  is  shown  by  the  oblique  line, 
the  stature  of  children  by  the  dotted  curve,  and  the  mean  stature  of 
the  race  in  the  horizontal  dotted  line. 

Statistical  vs.  physiological  methods. — One  of  the  chief  aims  and 
results  of  statistical  studies  is  to  eliminate  individual  peculiarities  and 
to  obtain  general  and  average  results.  Such  work  may  be  of  great 
importance  in  the  study  of  heredity,  especially  where  questions  of  the 
occurrence  or  distribution  of  particular  phenomena  are  concerned; 
but  the  causes  of  heredity  are  individual  and  physiological,  and 
averages  are  of  less  value  in  finding  the  causes  of  such  phenomena  than 
is  the  intensive  study  of  individual  cases. 

By  observation  alone  it  is  usually  impossible  to  distinguish  between 
inherited  and  environmental  resemblances  and  differences,  and  yet 
this  distinction  is  essential  to  any  study  of  inheritance.  If  all  sorts 
of  likenesses  and  unlikenesses  are  lumped  together,  whether  inherited 
or  not,  our  study  of  inheritance  can  only  end  in  confusion.  The 
value  of  statistics  depends  upon  a  proper  classification  of  the  things 
measured  and  enumerated,  and  if  things  which  are  not  commensur- 
able are  grouped  together  the  results  may  be  quite  misleading  and 
worthless. 

Statistical  studies  insufficient. — Unfortunately  Galton  and  Pear- 
son, as  well  as  some  of  their  followers,  have  not  always  carefully  dis- 
tinguished between  hereditary  and  environmental  characters.  Fur- 
thermore much  of  their  material  was  drawn  from  a  general  population 
in  which  were  many  different  families  and  lines  not  closely  related 
genetically.  Consequently  their  statistical  studies  are  of  little  value 
in  discovering  the  physiological  principles  or  laws  of  heredity.  Jen- 
nings (1910)  well  says,  ^'Galton's  laws  of  regression  and  of  ancestral 
inheritance  are  the  product  mainly  of  a  lack  of  distinction  between 
two  absolutely  diverse  things,  between  non-inheritable  tluctuations 
on  the  one  hand,  and  permanent  genotypic  differentiations  on  the 
other."  In  the  case  of  man  we  have  few  certain  tests  to  determine 
whether  the  differential  cause  of  any  character  is  hereditary  or  environ- 
mental, but  in  the  case  of  animals  and  plants,  where  experiments  may 
be  performed  on  a  large  scale,  it  is  possible  to  make  such  tests  by  (i) 
experiments  in  which  the  environment  is  kept  as  uniform  as  possible 
while  the  hereditary  factors  differ,  and  (2)  experiments  in  which,  in  a 


374     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

series  of  cases,  the  hereditary  factors  are  fairly  constant  while  the 
environment  differs.  In  this  way  the  differential  cause  or  causes  of 
any  character  may  be  located  in  heredity,  in  environment,  or  in  both. 
The  observational  and  sta^tistical  study  of  inheritance  helped  to 
outline  the  problem  but  did  little  to  solve  it.     Certain  phenomena  of 


Fig.  66. — Scheme  to  illustrate  Galton's  "Law  of  Filial  Regression"  as  shown 
in  the  stature  of  parents  and  children.  The  mean  height  of  all  parents  is  shown 
by  the  dotted  line  between  68  and  69  inches.  The  circles  through  which  the 
diagonal  line  runs  represent  the  heights  of  graded  groups  of  parents,  and  the  arrow- 
heads indicate  the  average  heights  of  their  children.  The  offspring  of  undersized 
parents  are  taller  and  of  oversized  parents  are  shorter  than  their  respective  parents. 
{From  Conklin,  after  Walter.) 


hereditary  resemblances  between  ascendants  and  descendants  were 
made  intelligible,  but  there  were  many  peculiar  and  apparently  irregu- 
lar or  lawless  phenomena  which  could  not  be  predicted  before  they 
occurred  nor  explained  afterward.  For  example  when  Darwin 
crossed  different  breeds  of  domestic  pigeons,  no  one  of  which  had  a 
trace  of  blue  in  its  plumage,  he  sometimes  obtained  offspring  with 


BIOMETRY  375 

more  or  less  of  the  blue  color  and  markings  of  the  wild  rock  pigeon 
from  which  domestic  pigeons  are  presumably  descended.  He  described 
many  cases  of  dogs,  cattle  and  swine,  as  well  as  many  cultivated 
plants,  in  which  offspring  resembled  distant  ancestors  and  differed 
from  nearer  ones;  such  cases  had  long  been  known  and  were  spoken 
of  as  '' reversion."  He  observed  many  cases  in  which  certain  charac- 
ters of  one  parent  prevailed  over  corresponding  characters  of  the 
other  parent  in  the  offspring,  this  being  known  as  ''prepotency"; 
but  there  was  no  satisfactory  explanation  of  these  curious  phenomena. 
They  did  not  come  under  either  of  Galton's  laws,  and  their  occur- 
rence was  apparently  so  irregular  that  every  such  case  seemed  to  be 
a  law  unto  itself. 


CHAPTER  XXVI 

HEREDITY  IN  PURE  LINES 
H.  H.  Newman 

In  the  last  chapter  we  have  seen  how  Galton  formulated  his  law 
of  filial  regression,  which  means  that  average  parents  tend  to  produce 
average  offspring,  but  that  exceptional  parents  tend  to  produce  off- 
spring less  exceptional  than  themselves,  but  nevertheless  more  excep- 
tional than  the  average. 

In  studying  this  law  the  Danish  botanist  Johanssen  saw  in  it  a 
possibiHty  of  racial  improvement  through  the  instrumentahty  of  con- 
trolled selection.  He  thought  that  by  continually  selecting  the  most 
exceptional  parents  in  each  generation  the  degree  of  regression  toward 
the  average  might  be  lessened  until  a  pure  non-regressing  strain  might 
be  produced. 

In  order  to  simplify  the  experiment  and  obviate  the  complexities 
inherent  in  intercrossing,  he  selected  a  self-fertilizing  type,  using  the 
bean  Phaseolus.  Taking  a  set  of  nineteen  beans  from  several  plants, 
choosing  the  largest  bean,  the  smallest  bean,  and  seventeen  inter- 
mediate types,  he  planted  these,  expecting  to  find  that  the  bean  pro- 
geny of  the  large  bean  would  be  mainly  large,  those  of  the  small  bean, 
small.  In  this  he  was  disappointed,  for  the  bean  progeny  of  the  large 
bean  fluctuated  about  a  mean,  some  being  large,  some  small,  but  the 
majority  average.  Similarly  the  bean  progeny  of  the  smallest  bean 
were  of  various  types,  mainly  average.  Each  of  these  nineteen  pure  lines 
had  a  mean  of  its  own,  and  irrespective  of  which  one  was  selected  (the 
largest,  the  smallest,  or  the  average)  the  mean  and  distribution  of  the 
progeny  was  practically  the  same.  Thus  it  was  concluded  that  within 
a  pure  line  selection  had  no  effect  in  modifying  the  character  of  size  of 
beans.  The  reason  for  this  rather  unexpected  result  is  not  far  to  seek. 
Johanssen  was  selecting  on  the  basis  of  somatic  variations,  the  fluctuat- 
ing variations  of  Darwin,  that  are  merely  due  to  more  or  less  favorable 
growth  conditions  and  are  not  represented  in  the  germ  plasm,  i.e.,  are 
not  hereditary.  Each  germ  cell  in  a  pure  line  is  supposed  to  have  the 
same  hereditary  units,  and,  if  that  is  so,  selection  would  not  be  expected 
to  effect  any  modification  that  would  persist. 

376 


HEREDITY  IX  PURE  LINES  377 

Johanssen  pointed  out  that  each  pure  line  had  a  dilTerent  mean 
size  of  bean  and  a  different  distribution  about  the  mean.  This  was  a 
real  hereditary  difference  due  to  differences  in  the  germinal  content 
of  the  original  parent-beans.  Two  beans  of  exactly  the  same  size,  one 
an  average  individual  of  a  larger  stock  and  one  a  large  individual  of  a 
smaller  stock,  were  planted  and  their  offspring  varied  about  two  dis- 
tinct means.  This  leads  to  the  idea  that  an  individual  produces  off- 
spring not  in  accord  with  its  somatic  appearance,  but  according  to  its 
germinal  content.  So  this  idea  of  the  difference  between  what  an 
individual  is  somatically,  and  what  it  is  germinally  led  Johanssen  to 
introduce  the  terms  ''phenotypic"  and  "genotypic" — "phenotype" 
and  "genotype." 

Thus,  if  one  selected  all  the  beans  of  a  given  size  he  would  have  a 
group  of  phenotypes  that  would  be  identical  pJienotypicaUy,  but  would 
be  very  different  genotypically;  for  each  might  be  germinally  different 
and  would  therefore  have  different  groups  of  offspring.  All  of  the 
individuals  in  one  pure  line,  however,  whether  they  differ  somatically 
{phenotypically)  or  not,  would  belong  to  the  same  genotype  and  would 
be  genotypically  equivalent. 

The  appreciation  of  this  distinction  at  this  place,  before  the  treat- 
ment of  Mendelian  heredity,  will  be  of  great  advantage.  Few  more 
useful  terms  have  been  devised  in  connection  with  genetics  than  geno- 
type and  phenotype. 

W.  L.  Tower  in  a  long  series  of  experiments  on  the  potato  beetle 
(Leptinotarsa  decemlineata)  came  to  similar  conclusions  as  the  result 
of  his  attempts  to  modify  a  character  by  selection.  Instead  of  using 
a  self-fertilizing  type,  he  chose  a  long  inbred  stock  that  was  probably 
all  identical  germinally,  but  varied  considerably  in  shade  of  color,  etc. 
He  selected  for  twelve  generations  the  darkest  specimens  and,  instead 
of  getting  all  dark  offspring,  he  got  an  array  of  all  shades  lluctuating 
evenly  about  the  average.  At  the  end  of  twelve  generations  of 
selection  there  was  no  change  in  the  proportion  of  light  and  dark 
individuals. 

Jennings  tried  another  type  of  pure-line  work,  using  one-celled 
organisms  which  reproduce  by  binary  fission,  i.e.,  by  the  division  of  the 
parent  into  two  nearly  equal  halves,  thus  forming  two  offspring.  He 
chose  a  considerable  number  of  Paramecia  and  isolated  each  in  a 
separate  small  aquarium  where  it  was  allowed  to  breed  for  some  gen- 
erations. The  original  individuals  differed  quite  markedly  in  size  and 
in  other  structural  characters.     The  various  sets  of  progeny  were 


378     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

measured  and  curves  of  variability  made  for  each.  It  was  found  that  a 
different  curve  and  mean  resulted  in  each  set.  If  the  largest  and  the 
smallest  individual  in  any  pure  line  is  isolated  and  allowed  to  produce 
a  set  of  progeny,  the  mean  and  curve  of  variability  will  be  the  same, 
because  both  the  large  and  the  small  individual  belong  to  the  same 
genotype,  though  varying  phenotypically. 

In  conclusion  therefore  we  may  say  that,  according  to  Johanssen, 
organisms  that  appear  to  be  alike,  or  are  alike  somatically,  are  identi- 
cal phenotypically;  but  organisms,  whether  alike  somatically  or  not, 
that  have  the  same  determiners  are  genotypically  identical  or  belong  to 
the  same  genotype. 

ARE   DETERMINERS    (gENES)    CONSTANT   OR  VARIABLE? 

In  our  study  of  the  causes  of  mutations  we  were  forced  to  admit 
that  we  are  almost  wholly  ignorant  of  the  causes  of  mutations.  We 
infer  that  in  the  majority  of  cases  the  change  occurs  within  the  germ 
cell  and  in  the  gene  itself.  In  this  pure-hne  work  where  the  genes  are 
unmixed  by  intercrossing  we  should  have  a  splendid  opportunity  of 
testing  the  possibility  of  genes  varying  or  becoming  modified.  In 
none  of  these  experiments  in  pure  Unes  was  there  any  indication  of 
genes  being  modified,  but  some  further  work  by  Jennings  seems  to 
imply  that  he  has  changed  his  position  with  reference  to  the  modifi- 
ability  of  genes.  Using  another  protozoan,  Difflugia,  he  found  that 
he  did  succeed  in  markedly  shifting  the  mean  by  selection,  and  thus 
seemed  to  prove  that  genes  were  modifiable.  This  work  is  open  to  two 
comments.  First,  protozoa  are  not  suitable  material  for  testing  the 
distinction  between  germinal  and  somatic  changes,  because  the  whole 
individual  is  but  a  single  cell;  therefore  any  change  that  is  passed  on 
may  be  merely  a  somatic  change.  Second,  Jennings,  in  making  his 
selections,  did  so  on  the  basis  not  so  much  of  an  individual  itself  as 
upon  the  characters  of  its  ancestors  for  some  generations  back.  He 
was,  therefore,  working  more  with  genotypic  than  with  phenotypic 
considerations.  If,  as  he  claims,  there  was  a  progressive  modification 
of  characters,  such  as  numbers  of  spines,  beyond  the  limit  of  vari- 
ability in  the  original  stock,  the  results  would  seem  to  warrant  the 
conclusion  that  genes  are  variable  and  that  selection  might  be  effective 
in  establishing  new  types  within  pure  lines. 

Castle,  as  the  result  of  a  long  and  elaborate  experiment  with 
"hooded  rats,"  at  first  thought  that  the  gene  for  the  hooded  pattern 
was  variable  and  could  be  enhanced  by  selection;   later,  however,  he 


HEREDITY  IN  PURE  LIXES  379 

says  that "  the  changes  in  question  had  not  occurred  in  the  gene  for  the 
hooded  pattern,  but  in  the  residual  heredity."  The  situation  api:)ears 
to  be  this:  the  hooded  pattern  is  a  black  marking  covering  the  head 
and  shoulders  of  the  otherwise  white  body.  It  varies  in  the  extent  to 
which  it  covers  the  body,  and,  by  selecting  the  plus  or  minus  indi- 
viduals, a  nearly  complete  black  and  a  nearly  complete  white  race  was 
produced.  These  were  maintained  in  a  pure  line  for  three  generations 
and  then  were  bred  with  a  pure  white  strain.  After  six  generations 
''  the  whitest  individuals  extracted  from  the  dark  hooded  race  were  no 
darker  than  the  darkest  individuals  extracted  from  the  white  hooded 
race.  In  other  words  repeated  crossing  with  the  non-hooded  (wild) 
race  had  caused  the  changes  in  the  hooded  character,  which  had  been 

secured  by  selection,  altogether  to  disappear Accordingly  we 

are  led  to  conclude  that  unit-characters  or  genes  are  remarkably  con- 
stant and  that  when  they  seem  to  change  as  the  result  of  hybridization 
or  of  selection  unattended  by  hybridization,  the  changes  are  rather  in 
the  total  complex  of  factors  concerned  in  heredity  than  in  single  genes." 

In  a  mutating  race,  however,  such  as  Drosophila,  changes  in  genes 
surely  Jo  occur,  as  has  been  proved  by  the  work  of  Morgan  and  his 
collaborators.  We  do  not  know  what  causes  changes  in  genes,  but 
we  can  demonstrate  that  they  do  occur.  Selection  cannot  bring  about 
any  change  in  single  genes,  but  can  only  result  in  isolating  certain  sets 
of  genes  in  a  single  pure  line.  This  once  done,  selection  ceases  to  be 
effective  in  altering  the  character  of  the  stock  under  selection. 

"The  substance  of  our  present  knowledge  as  to  changes  in  genes," 
concludes  Castle,  "may  be  summed  up  in  the  statement  that  such 
changes  come  or  go  suddenly  in  their  entirety,  and  cannot,  so  far  as 
we  know,  be  influenced  by  selection  or  any  other  controllable  process. 
Hence  we  may  call  changes  in  genes  mutations." 


CHAPTER  XXVII 
MENDEL'S  LAWS  OF  HEREDITY^ 

J.    ARTHUR   THOMSON 

Mendel's  life  and  character 

Gregor  Johann  Mendel  was  born  in  1822,  the  son  of  well-to-do 
peasants  in  Austrian  Silesia.  He  became  a  priest  in  1847,  and  studied 
physics  and  natural  science  at  Vienna  from  1851  to  1853.  Thence  he 
returned  to  his  cloister  and  became  a  teacher  in  the  Realschule  at 
BrUnn.  It  was  his  hobby  to  make  hybridisation  experiments  with 
peas  and  other  plants  in  the  garden  of  the  monastery,  of  which  he 
eventually  became  abbot.  Apart  from  two  papers,  one  dealing  with 
peas  and  a  shorter  one  with  hawkweeds,  and  some  meteorological 
observations,  he  does  not  seem  to  have  published  much.  But  what 
he  did  publish,  if  small  in  quantity,  was  large  in  quality.  He  died  in 
1884. 

Mendel's  discoveries 

In  1866  Gregor  Johann  Mendel,  Abbot  of  Briinn,  published  what 
some  regard  as  one  of  the  greatest  of  biological  discoveries.  After 
many  years  of  patient  experimenting,  chiefly  with  the  edible  pea,  he 
reached  a  very  important  conclusion  in  regard  to  the  inbreeding  of 
hybrids,  which  is  often  briefly  referred  to  as  "Mendel's  Law."  His 
publication  was  practically  buried  in  the  Proceedings  of  the  Natural 
History  Society  of  Briinn;  those  who  knew  of  it,  as  Nageli  for  instance 
did,  failed  to  realise  its  importance:  in  fact,  Mendel's  epoch-making 
work  was  lost  sight  of  amid  the  enthusiasm  and  controversy  which  the 
promulgation  of  Darwinism  (1858)  had  evoked.  Mendel's  Law  seems 
to  have  been  rediscovered  independently  in  1900  by  the  botanists, 
De  Vries,  Correns,  and  Tschermak;  and  to  Mr.  Bateson  we  owe  much, 
not  only  for  his  recognition  of  the  far-reaching  importance  of  the 
abbot's  work,  but  also  for  a  notable  series  of  experiments  in  which  he 
has  confirmed  and  extended  it. 

^  From  J.  Arthur  Thomson,  Heredity  (copyright  1907).  Used  by  special 
permission  of  the  publishers,  John  Murray,  London. 

380 


MENDEL'S  LAWS  OF  HEREDITY  381 

Mendel's  experiments.— What  Mendel  sought  to  discover  was  the 
law  of  inheritance  in  hybrid  varieties,  and  he  selected  for  experiment 
the  edible  pea  {Pistim  sativum).  The  trial  plants,  he  says,  must 
possess  constant  differentiating  characters,  and  must  admit  of  easy 
artificial  pollination;  the  hybrids  of  the  plants  must  be  readily  fertile, 
and  readily  protectable  from  the  influence  of  foreign  pollen.  These 
conditions  were  afforded  by  peas,  and  twenty-two  varieties  or  sub- 
species of  pea  were  selected,  which  remained  constant  during  the  eight 
years  of  the  experiments.  Whether  they  were  called  species,  or  sub- 
species, or  varieties,  is  a  matter  of  convenience;  the  names  Pisum 
quadratum,  P.  saccharatum,  P.  umbcUatwn,  etc.,  do  in  any  case  repre- 
sent groups  of  similar  individuals  which  breed  true  inter  se.  It  should 
be  noted  that  these  peas  have  the  particular  advantage,  for  experi- 
mental purposes,  that  they  are  habitually  self-fertihsed — in  North 
Europe,  at  least. 

In  studying  the  different  forms  of  peas,  Mendel  found  that  there 
were  seven  differentiating  characters  which  could  be  relied  on : 

1.  The  form  of  the  ripe  seeds,  whether  roundish,  with  shallow 
wrinkles  or  none,  or  angular  and  deeply  wrinkled: 

2.  The  colour  of  the  reserve  material  in  the  cotyledons — pale 
yellow,  bright  yellow,  orange,  or  green; 

3.  The  colour  of  the  seed-coats,  whether  white,  as  in  most  peas 
with  white  flowers,  or  grey,  grey-brown,  leather  brown,  with  or  with- 
out violet  spots,  and  so  on; 

4.  The  form  of  the  ripe  pods,  whether  simply  inflated,  or  con- 
stricted, or  wrinkled; 

5.  The  colour  of  the  unripe  pods,  whether  light  or  dark  green,  or 
vividly  yellow,  this  colour  being  correlated  with  that  of  stalk,  leaf- 
veins,  and  blossoms; 

6.  The  position  of  the  flowers,  whether  axial  or  terminal;    and 

7.  The  length  of  the  stem,  whether  tall  or  dw^arfish. 
Mendel's  results;   the  Law  of  Dominance. — Having  defined  the 

-differentiating  characteristics  of  the  varieties,  Mendel  proceeded  to 
make  crosses  between  these,  investigating  one  character  at  a  time. 
Thus,  pollen  from  a  pea  of  the  round-seeded  variety  was  transferred 
to  the  stigma  of  a  pea  of  the  angular-seeded  variety,  the  stamens  of  the 
artificially  pollinated  flower  being,  of  course,  removed  before  they 
were  ripe.     The  same  was  done  all  along  the  line. 

What  was  the  result  in  the  hybrid  or  cross-bred  offspring  ?  It  was 
found  that  they  sliowed  one  of  each  pair  of  contrasted  characters,  to 


382      READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

the  total,  or  almost  total,  exclusion  of  the  other.     No  intermediate 
forms  appeared. 

Mendel  called  the  character  that  prevailed  dominant,  and  the 
character  that  was  suppressed,  or  apparently  suppressed,  recessive. 
And  the  first  big  result  was  that  crosses  between  a  plant  with  the 
dominant  character  and  a  plant  with  the  recessive  character  yielded 
offspring  all  resembling  the  dominant  parent  as  regards  the  character 
in  question.  Let  us  for  shortness  call  the  parents  D  and  R,  and  the 
first  result  may  be  expressed  thus:  DXR  =  D. 

It  must  be  carefully  noted  that  the  complete  dominance  which 
Mendel  observed  has  been  shown  in  other  cases  to  be  the  exception 
rather  than  the  rule.  Thus  a  cross  between  a  "  Chinese  "  primula  with 
wavy  crenated  petals  and  a  "star"  primula  with  flat  simply  notched 
petals  is  intermediate  between  the  two  parents;  and  yet,  as  the  next 
generation  shows,  the  case  is  one  of  Mendelian  inheritance. 

In  many  cases  the  hybrid,  while  on  the  whole  dominant,  may  show 
some  influence  of  the  recessive  character  but  not  nearly  enough  to 
warrant  us  in  speaking  of  a  blend.  Thus,  when  white  (dominant) 
Leghorn  poultry  are  crossed  with  brown  (recessive)  Leghorn,  most  of 
the  offspring  have  some  *' ticks"  of  colour.  When  these  are  inbred 
they  produce  a  quarter  brown  (extracted  recessives)  and  three- 
quarters  pure  white  or  white  with  a  few  ticks.  The  dominance  is  not 
quite  perfect. 

The  Law  of  Splitting  or  Segregation. — In  the  next  generation  the 
cross-bred  plants  (products  of  D  and  R,  or  R  and  D,  but  all  apparently 
like  D)  were  allowed  to  fertilise  themselves,  with  the  result  that  their 
offspring  exhibited  the  two  original  forms,  on  the  average  three  domi- 
nants to  one  recessive.  Out  of  1,064  plants,  787  were  tall,  277  were 
dwarfs. 

When  these  recessive  dwarfs  were  allowed  to  fertilise  themselves 
they  gave  rise  to  recessives  only,  for  any  number  of  generations.  The 
recessive  character  bred  true. 

When  the  dominants,  on  the  other  hand,  were  allowed  to  fertilise 
themselves,  one-third  of  them  produced  "pure"  dominants,  which  in 
subsequent  generations  gave  rise  to  dominants  only;  and  two- thirds 
of  them  produced  once  again  the  characteristic  mixture  of  dominants 
and  recessives  in  the  proportion  of  3 :  i . 

The  general  results  may  be  expressed  in  the  scheme.  The 
result  of  the  hybridisation  is  a  generation  (Fi)  like  the  dominant 
parent.     They  may  be  represented  by  the  symbol  D(R),  for  they 


MENDEL'S  LAWS  OE  HEREDITY 


383 


D$XR^or  R?XD^ 

\     / 


Parent-forms  (P') 


D(I<)       .....     Hybrid-ofTspring  (F«) 


3D 

II 


I  R     .      Generation  of  inbred  h\bri<is  fp) 


I  D 


+ 


2D(R) 


D 


3D 


iR     R 


I  D     +     2  D(R) 


D      D 


D      D 


3D 


(F3) 


I  D  +  2D(R) 
D 


iR      R     R 


R     R     R 


(F4) 


(F5) 


carry  with  them  the  possibility  of  having  offspring  with  the  recessive 
character;  that  is  to  say,  the  recessive  character  remains  latent  in 
the  inheritance. 

When  these  D(R)s  are  inbred  (self- fertilised,  in  the  case  of  peas) 
they  have  offspring  (F2),  some  of  which  resemble  the  recessive  parent, 
while  others  resemble  the  dominant  parent,  and  these  occur  in  the 
proportion  of  1:3.  When  those  resembling  the  recessive  parent  are 
inbred,  they  breed  true — i.e.,  they  give  rise  to  a  line  of  pure  recessives. 
Those  resembling  the  dominant  parent  are  all  apparently  alike,  but 
their  subsequent  history  shows  that  they  may  be  divided  into  a  set 
which  breed  true  to  the  dominant  type  and  a  set  which  behave  like  the 
first  generation  of  hybrids — i.e.,  they  go  on  sphtting  up  into  dominant- 
like forms  and  pure  recessives.  These  two  sets  occur  in  the  propor- 
tions of  1:2. 

A  case  of  peas. — Let  us  consider  a  concrete  case.  Peas  with 
rounded  seeds  were  crossed  with  peas  having  angular  wrinkled  seeds. 
In  the  offspring  the  character  of  roundness  was  dominant ;  the  angular 
wrinkled  character  had  disappeared  or  receded.  It  was  not  lost,  as 
the  next  generation  showed. 

The  hybrid  offspring,  all  with  rounded  seeds,  were  allowed  to  self- 
fertilise.  In  their  progeny  roundish  seeds  and  angular  wrinkled  seeds 
occurred  in  the  proportions  of  3:1.  Here  were  the  recessives  again, 
and  when  they  were  allowed  to  self-fertilise  they  produced  pure  reces- 
sives only,  with  angular  wrinkled  seeds. 


384     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 


The  dominants,  however,  were  not  all  pure  dominants,  for  when 
they  were  allowed  to  self -fertilise  they  produced  one-third  pure  domi- 
nants and  two-thirds  "impure"  dominants,  the  latter  being  distin- 
•guished  by  the  fact  that  in  their  offspring  recessives  reappeared  in  the 
proportion  of  one  recessive  to  three  dominants. 

The  outstanding  facts,  taking  the  case  of  yellow-seeded  and  green- 
seeded  peas,  may  be  thus  summarised: — 


Parental 

Generation  (Pi) 


First  Filial  (hybrid) 
Generation  (Fi) 


Yellow-seeded  "pure" 
plant  (dominant) 


Green-seeded  "pure" 
plant  (recessive) 


All  the  offspring  were  yellow-seeded 
Self-fertilised  they  yielded 


Second  Filial  {inbred)      Yellows 
Generation  (F2)         (pure  type) 


Yellows 
(impure  type) 


Greens 
(pure  type) 


Third  Filial  {inbred)        Yellows        Yellows         Yellows       Greens  Greens 

Generation  (F3)         (pure  type)        (pure)         (impure)       (pure)        (pure  type) 


Thus  intercrossing  of  forms  with  contrasted  characters  results  not 
in  transitional  blends,  but  in  the  dominance  of  one  character  and  the 
recession  of  another.  Self-fertilisation  (the  extreme  of  inbreeding) 
of  the  hybrids  results  in  a  number  of  pure  recessives  and  a  number  of 
dominants  in  the  proportion  1:3;  some  of  these  dominants  (one-third) 
are  pure,  and  produce  only  dominants;  some  (two-thirds)  are  appar- 
ently pure,  but  produce  dominants  and  recessives  in  the  old  propor- 
tion, 3:1. 

A  case  of  mice. — Let  us  take  a  concrete  case  from  among  animals. 
A  grey  house-mouse  is  crossed  with  a  white  mouse;  the  offspring  are 
all  grey.     Greyness  is  dominant;  albinism  is  recessive. 


(P') 


1  G         2  G(W) 


I  W 


W 


(F3) 


MENDEL'S  LAWS  OF  HEREDITY  385 

The  grey  hybrids  are  inbred;  their  ofTsj^ring  are  grey  and  white 
in  the  proportion  3:1.  If  these  whites  are  inbred  they  show  them- 
selves "pure,"  for  they  produce  whites  only  for  subsequent  genera- 
tions. But  when  the  greys  are  inbred  they  show  themselves  of  two 
kinds,  for  one-third  of  them  produce  only  greys,  which  go  on  produ- 
cing greys;  while  the  other  two-thirds,  apparently  the  same, produce 
both  greys  and  whites.     And  so  it  goes  on. 

Summary. — In  his  exceedingly  clear  exposition  of  Mendelism 
(1905)  Mr.  R.  C.  Punnett  states  the  result  thus:  "Wherever  there 
occurs  a  pair  of  differentiating  characters  of  which  one  is  dominant 
to  the  other,  three  possibilities  exist:  there  are  rccessives  which 
always  breed  true  to  the  recessive  character;  there  are  dominants 
which  breed  true  to  the  dominant  character,  and  are  therefore  pure; 
and  thirdly,  there  are  dominants  which  may  be  called  impure,  and 
which  on  self-fertilisation  (or  in-breeding,  where  the  sexes  are  separate) 
give  both  dominant  and  recessive  forms  in  the  fixed  proportion  of 
three  of  the  former  to  one  of  the  latter." 

Schematic  representation  of  Mendel's  Law. — Following  Mr. 
Punnett's  suggestion,  with  slight  modifications,  we  may  use  the  sym- 
bols Pi,  P2,  P3  for  the  parental,  grandparental,  and  great-grandparental 
generations;  Fi  for  the  first  filial  (hybrid)  generations,  F^,  F3,  F4 
for  the  subsquent  inbred  generations.  The  symbol  D(R)  means  a 
dominant  with  the  recessive  character  unexpressed,  but  potentially 
present;  DD  or  RR  means  pure  "extracted"  dominants  or  reces- 
sives — i.e.,  those  pure  forms  which  are  sifted  out  from  the  inbreed- 
ing of  "impure"  dominants. 

D       R    .      .      .     P^ — great-grandparental  generation 

D        R    .      .      .     P' — grandparental  generation 

I  I 

D       R    .      .      .     P' — parental  generation 

D(R)      .      .      .     F'— first  filial  (hybrid)  generation 


I  DD  2  D(R)  I  RR     .  F»— second    filial    (in- 

"  Extracted "  pure       Impure  dominants    Pure  recessives  bred)  generation 

dominants  I 

I      I \  I 

DD    I  DD  2  D(R)  I  RR   RR     .  F^— third  generation 


DD     DD     I  DD     2  D(R)     i  RR     RR     RR     .     F*— fourth  generation 


386     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

Mendel's  explanations^ 

JOHN   M.    COULTER   AND   MERLE   C.    COULTER 

Mendel's  explanation  of  this  behavior  involved  three  theses  which 
at  that  time  were  new  to  biology.  These  theses  must  be  kept  distinct 
from  one  another. 

1.  Independent  unit  characters. — This  means  that  an  organism, 
although  representing  a  morphological  and  physiological  unity,  from 
the  standpoint  of  heredity  is  a  complex  of  a  large  number  of  independ- 
ent heritable  units.  Thus  if  one  pea  plant  is  tall  and  another  one  is 
dwarf  the  behavior  of  the  hybrid  produced  from  them  with  reference 
to  this  character  will  be  the  same,  no  matter  what  other  characters 
the  parent  plants  may  have  had.  In  other  words,  the  characters 
are  mdeperident  units,  unaffected  by  other  characters  or  units.  The 
character  of  tallness  from  a  tall  plant  with  wrinkled  seeds  or  purple 
flowers  will  act  just  the  same  as  from  a  tall  plant  with  smooth  seeds 
or  white  flowers.  Tallness  is  a  unit  and  its  behavior  in  inheritance  is 
independent  of  all  other  units. 

2.  Dominance. — In  the  germ  plasm  there  are  certain  determiners 
of  unit  characters  which  dominate  during  the  development  of  the 
body,  causing  these  characters  to  dominate  over  others  and  thus 
become  visible.  The  characters  dominated  over  and  thus  not  allowed 
to  express  themselves  are  called  recessive  characters.  These  recessive 
characters  are  present  in  the  germ  plasm,  but  cannot  express  them- 
selves and  become  visible  as  long  as  the  dominant  characters  are  pres- 
ent. When  a  dominant  character  is  absent,  however,  its  recessive 
alternate  is  free  to  express  itself  and  become  visible. 

For  example,  in  the  case  of  tall  and  dwarf  peas,  tallness  is  a  domi- 
nant character  and  dwarfness  is  its  alternative  recessive.  When  a 
dwarf  appears,  therefore,  there  is  present  no  dominant  tallness  to 
suppress  it.  In  the  Fi  generation  all  the  individuals  were  tall  because, 
although  they  had  all  received  the  recessive  character  of  dwarfness 
from  one  of  the  parents,  they  had  received  the  dominant  character 
of  tallness  from  the  other  parent,  and  so  dwarfness  did  not  appear  in 
any  of  them.  Such  pairs  of  alternative  characters  are  now  commonly 
called  allelomorphs.  Thus  tallness  and  dwarfness  are  allelomorphs 
in  the  pea,  one  dominant  over  the  other,  which  is  therefore  recessive. 

3.  Purity  of  gametes. — A  gamete  can  contain  only  one  of  two 
alternative  characters.     For  example,  it  may  contain  the  character 

^  From  Coulter  and  Coulter,  Plant  Genetics  (The  University  of  Chicago  Press 
copyright  19 18). 


MENDEL'S  LAWS  OF  HEREDITY  387 

for  tallness  or  for  dwarfness,  but  not  both.  In  other  words,  allelo- 
morphs cannot  be  represented  in  the  same  gamete.  If  the  gamete 
having  the  character  for  tallness  unites  with  one  having  the  character 
for  dwarfness,  the  resulting  zygote  will  contain  both,  but  will  produce 
a  tall  individual  because  tallness  is  dominant  over  dwarfness.  When 
this  tall  hybrid  produces  gametes,  however,  one-half  of  them  will 
contain  the  character  for  dwarfness.  Thus  the  alternative  characters 
are  ''segregated"  in  gamete  formation  and  no  gamete  will  have  both 
characters. 

These  three  theses,  independent  unit  characters,  dominance,  and 
purity  of  gametes  (better  called  segregation),  make  up  the  theoretical 
explanation  of  Mendel's  law.  Independent  unit  characters  was  of 
course  a  necessary  conception.  It  was  original  with  Mendel,  and  has 
also  been  original  with  other  investigators,  but  this  conception  does  not 
represent  the  essential  feature  of  Mendel's  law.  The  idea  of  domi- 
nance had  been  somewhat  vaguely  proposed  before  Mendel's  time. 
In  the  old  literature  on  animal  breeding  one  meets  theories  of  pre- 
potency, which  were  proposed  again  and  again  before  the  discovery 
of  Mendel's  work  in  1900.  In  any  event  Mendel  was  the  first  to 
formulate  definitely  the  theory  of  dominance  among  unit  characters. 
It  should  be  realized  also  that  dominance  is  not  an  essential  feature  of 
Mendel's  theory.  Many  cases  are  known  in  which  dominance  fails, 
but  in  other  regards  the  Mendelian  inheritance  is  strictly  followed. 

The  essential  feature  of  Mendel's  theory  is  his  conception  of  the 
purity  of  gametes,  brought  about  by  the  segregation  of  alternative 
characters.  The  striking  fact  is  that  this  conception,  purely  theoreti- 
cal with  Mendel,  has  since  been  confirmed  by  cytology.  In  the 
mechanism  of  cell  division  each  chromosome  is  divided  into  two  equal 
parts  and  each  daughter-cell  receives  one  of  these  parts.  It  is  a 
reasonable  inference  that  chromosomes  are  bearers  of  hereditary 
characters.  In  the  production  of  gametes  the  number  of  chromosomes, 
characteristic  of  the  organism  is  reduced  one-half.  As  a  consequence 
each  gamete  carries  only  one-half  the  characters  of  the  individual  that 
produced  it.  An  application  of  these  statements  to  an  explanation  of 
Mendel's  3 :  i  ratio  will  illustrate  the  situation. 

For  convenience  we  will  assume  that  the  nuclei  of  Mendel's  peas 
have  four  chromosomes  each  (Fig.  67).  In  the  case  of  a  tall  plant  two 
of  the  four  chromosomes  carry  the  character  for  tallness,  that  is,  some- 
thing that  determines  the  production  of  the  tall  character  in  the 
somatoplasm,  which  is  practically  the  body  builder.     This  unknown 


388     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

something  is  called  by  various  names  in  the  literature  of  genetics,  the 
commonest  one  being  determiner.  In  our  illustration,  therefore,  two 
of  the  four  chromosomes  carry  the  determiner  for  tallness.  At  this 
point  two  questions  may  be  asked. 

I.  Why  do  just  two  of  the  four  chromosomes  carry  the  determiner 
for  tallness  rather  than  all  of  them  or  only  one  of  them  ?  Just  here 
it  would  be  difficult  to  explain  why  no  more  than  two  of  the  four 
chromosomes  are  represented  as  carrying  the  same  determiner.  This 
will  be  explained  later.  It  is  easy  to  answer,  however,  why  the  deter- 
miner is  being  carried  by  more  than  one  chromosome.  When  gametes 
are  formed  the  chromosome  number  is  reduced  one-half.  Since  every 
gamete  from  a  pure  tall  plant  carries  the  determiner  for  tallness  there 


Dwarf  Parent 


Fig.  67. — Diagram  illustrating  behavior  of  chromosomes  in  Mendel's  cross 
of  tall  and  dwarf  peas.  Large  rectangular  figures,  nuclei  of  zygotes  or  mature 
individuals;  large  circles,  gametes;  small  circles  within  zygotes  and  gametes, 
chromosomes;  letters  on  chromosomes,  determiners  (T,  tallness;  D,  dwarf ness). 
{From  Coulter  and  Coulter.) 

must  have  been  at  least  two  chromosomes  carrying  the  determiner 
before  the  gametes  were  formed. 

2.  Do  these  two  chromosomes  carry  any  other  determiner  than 
that  for  tallness  ?  In  a  tentative  way  this  question  may  be  answered 
in  the  affirmative,  but  a  fuller  discussion  of  the  situation  must  be 
deferred.  There  is  much  experimental  evidence  that  indicates  that 
more  than  one  determiner  is  carried  on  a  single  chromosome.  In  some 
cases  also  there  are  more  Mendelian  determiners  than  there  are 
chromosomes. 

The  situation  is  represented  in  Fig.  67.  This  shows  a  somatic 
cell  with  the  diploid  or  2x  number  of  chromosomes.  In  the  formation 
of  gametes  this  number  is  reduced  to  the  haploid,  or  x  number,  which 
in  this  case  is  two.     The  diagram  shows  that  the  reduction  separates 


MENDEL'S  LAWS  OF  HEREDITY 


389 


(segregates)  the  two  chromosomes  carrying  the  character  for  tallness, 
so  that  each  gamete  contains  one.  This  occurs  for  the  other  characters 
as  well  as  for  that  of  tallness.  From  the  tall  plant,  therefore,  all  the 
gametes  will  contain  the  character  for  tallness,  and  from  a  dwarf  plant 
all  of  the  gametes  would  contain  the  character  for  dwarfness.  When 
these  two  individuals  are  crossed  the  zygote  will  contain  both  charac- 
ters, and  these  two  characters  will  be  transmitted  together  in  the 
succeeding  cell  generations.  The  individual  from  such  a  zygote  of 
course  would  be  tall,  but  at  the  same  time  it  would  be  carrying  a 
recessive  determiner  for  dwarfness,  and  this  fact  would  be  shown  by 


Q_0 


Fig.  68. — Diagram  illustrating  behavior  of  first  hybrid  generation  (Fi)  when 
inbred.  Illustrates  meaning  of  "segregation"  and  "purity  of  gametes"  and  how 
chance  matings  of  Fi  gametes  result  in  3:1  ratio  in  F2  generation;  dwarf  indi- 
vidual produced  only  by  zygote  in  lower  right-hand  corner.  {From  Coulter  and 
Coulter.) 

its  behavior  in  breeding.  The  result  of  inbreeding  such  hybrids  is 
indicated  in  the  accompanying  diagram  (Fig.  68),  which  represents 
the  chance  matings  of  two  kinds  of  gametes.  The  obvious  results  are 
three  tall  individuals  and  one  dwarf.  This  is  the  so-called  fnonohybrid 
ratio,  which  means  the  ratio  when  a  single  pair  of  allelomorphs  is 
considered. 

Before  discussing  the  further  development  of  Mendel's  law  it  will 
be  necessary  to  explain  some  of  the  terminology  of  genetics.  When 
each  gamete  carries  the  same  kind  of  determiner  the  zygote  is  said  to 
receive  a  double  dose;  when  a  zygote  receives  only  a  single  such  deter- 
miner it  is  said  to  receive  a  single  dose.  In  Fig.  68  one  zygote  receives 
a  double  dose  of  tallness  and  two  others  a  single  dose.  These  phrases 
are  more  or  less  common  in  the  literature  of  the  subject,  but  the  more 


390     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

frequent  terminolog>^  is  as  follows.  When  two  similar  gametes  unite 
to  form  a  zygote  it  is  called  a  homozygote;  when  the  two  pairing 
gametes  are  different  the  zygote  is  called  a  heterozygote.  Using  this 
terminology  it  is  evident  that  the  3:1  ratio  of  the  F2  generation  is 
really  a  1:2:1  ratio,  as  follows:  i  homozygote  for  the  dominant 
character,  2  heterozygotes,  and  i  homozygote  for  the  recessive  charac- 
ter. The  1:2:1  ratio  therefore  is  the  significant  one  and  appears  as  a 
3 : 1  ratio  only  because  of  dominance. 

In  the  experiment  represented  in  Fig.  68  three  tall  individuals 
appear  in  the  F2  generation.  Superficially  the  individuals  look  alike, 
but  it  is  realized  that  i  differs  from  the  other  2  in  germinal  constitu- 
tion, for  I  will  produce  only  one  kind  of  gamete,  while  the  other  2 
will  produce  two  kinds.  To  indicate  this  situation  Johannsen  has 
introduced  some  appropriate  terminology.  Organisms  which  seem 
to  be  alike,  regardless  of  their  germinal  constitution,  are  said  to  be 
phenotypically  alike,  or  to  belong  to  the  same  phenotype.  On  the 
other  hand,  organisms  having  identical  germinal  constitution  are  said 
to  be  genotypically  alike,  or  to  belong  to  the  same  genotype.  From 
the  standpoint  of  phenotypes  only,  Mendel's  F2  generation  shows  the 
3:1  ratio;  but  if  genotypes  are  considered,  it  shows  the  1:2:1  ratio. 
In  other  words,  this  group  of  forms  contains  two  phenotypes  but  three 
genotypes. 

Referring  again  to  Fig.  68  several  things  may  be  inferred.  It  can 
be  seen  what  will  happen  in  the  F3  generation  when  the  F2  individuals 
are  inbred.  The  dominant  homozygote  will  produce  only  dominant 
homozygotes  in  the  F3  generation  and  will  continue  to  produce  them 
as  long  as  it  is  inbred.  The  two  heterozygotes  will  split  up  in  the 
F3  generation  in  the  same  1:2:1  ratio  as  did  their  hybrid  parents  of  the 
Fi  generation.  The  recessive  homozygote  will  produce  only  recessive 
homozygotes  as  long  as  it  is  kept  pure  by  being  inbred. 

It  is  interesting  to  consider  what  will  happen  if  a  heterozygote 
form  is  crossed  with  a  homozygous  recessive.  It  should  be  obvious 
that  one-half  of  the  progeny  would  be  pure  recessives,  while  the  other 
aalf  would  be  heterozygotes,  that  is,  there  would  be  a  1:1  ratio.  A 
similar  result  would  be  obtained  by  crossing  a  heterozygote  with  a 
dominant  homozygote,  although  all  the  immediate  progeny  would 
show  the  dominant  character.  The  real  situation  would  be  revealed, 
however,  when  this  progeny  was  inbred,  for  one-half  would  be  homo- 
zygous (pure  breeders)  and  the  other  half  would  be  heterozygous 
(hybrid  breeders). 


MENDEL'S  LAWS  OF  HEREDITY  391 

Thus  far  we  have  considered  only  what  is  called  the  monohybrid 
ratio,  that  is,  the  ratio  obtained  from  one  pair  of  contrasting  charac- 
ters, such  as  tallness  and  dwarfness.  The  next  step  is  to  consider  the 
dihybrid  ratio.  Mendel  also  used  contrasting  seed  characters,  find- 
ing, for  example,  that  smoothness  in  seeds  is  dominant  to  a  wrinkled 
condition.  Introducing  this  pair  of  contrasting  characters  into  the 
situation  we  have  been  considering,  the  dihybrid  ratio  will  be  the 
result.  Crossing  a  tall,  smooth-seeded  individual  with  a  dwarf 
wrinkled-seeded  individual  it  is  evident  that  all  of  the  Fi  or  first  hybrid 
generation  will  be  tall,  smooth-seeded  individuals,  since  both  of  these 
characters  are  dominant.  In  the  F2  generation,  however,  the  follow- 
ing ratio  will  appear:  9  tall  smooth,  3  dwarf  smooth,  3  tall  wrinkled, 
I  dwarf  wrinkled;  which  is  a  9:3:3:1  ratio.  This  is  the  dihybrid 
ratio,  the  explanation  of  which  may  be  indicated  in  Fig.  69.  The 
question  may  be  raised  why  the  characters  for  tallness  and  smoothness 
are  not  represented  on  the  same  chromosome.  If  they  were,  the 
result  would  be  a  simple  monohybrid  ratio,  except  that  the  tall  indi- 
viduals would  always  be  smooth-seeded  as  well,  and  dwarfs  would  be 
always  wrinkled-seeded.  The  possibility  of  one  chromosome  carrying 
two  different  determiners  will  be  considered  later,  but  at  present  we 
shall  assume  that  these  determiners  are  on  different  chromosomes. 

Fig.  69  shows  that  we  are  dealing  with  two  homozygotes,  each  pro- 
ducing only  one  kind  of  gamete,  so  that  all  the  hybrid  progeny  will 
be  similar,  both  genotypically  and  phenotypically,  that  is,  with  the 
same  germinal  constitution  and  the  same  appearance.  By  inbreeding 
these  Fi  individuals,  it  will  be  seen  that  four  kinds  of  gametes  are 
involved.  Crossing  these  four  kinds  of  gametes  the  resulting  com- 
binations are  indicated  in  Fig.  69.  The  result  is  four  pheno types,  as 
follows:  Nos.  I,  2,  3,  4,  5,  7,  9,  10,  13  are  tall  smooth  individuals; 
Nos.  II,  12,  15  are  dwarf  smooth;  Nos.  6,  8,  14  are  tall  wrinkled; 
No.  16  is  dwarf  wrinkled.     This  is  the  9:3:3:1  ratio. 

It  will  be  noticed  that  Nos.  i,  6,  11,  16  are  homozygotes  and  there- 
fore will  breed  true;  but  the  rest  are  heterozygotes,  either  for  one  pair 
of  characters  or  for  both,  and  these  would  split  into  various  types  upon 
further  breeding. 

The  next  step  is  the  trihybrid  ratio.  Mendel  found  yellow  seeds 
dominant  over  green  seeds,  and  if  this  pair  of  characters  is  included 
with  those  used  above  the  trihybrid  result  can  be  observed.  The 
experiment  would  cansist  in  crossing  tall,  smooth,  yellow  individuals 
with  dwarf,  wrinkled,  green  individuals;    and  it  is  obvious  that  the 


392     RE.\DINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 


hybrid  progeny  would  all  be  tall,  smooth,  yellow,  since  these  three 
characters  are  dominant.  Inbreeding  the  hybrids  gives  the  following 
result  in  the  F2  generation:  27  tall  smooth  yellow,  9  tall  smooth  green. 


Dwarf  Wrinkled 
Parent 


Gametes 


®® 


®® 


®® 


®.® 
®® 


®  ® 


®,„® 
®® 


®,® 

(w)  (w 


T)  {^D 
S)'(S 


®'® 


®® 


®® 


®.® 


®»® 

®  ® 


®® 


®.® 

®  ® 


Fig.  69. — Diagram  illustrating  dihybrid  ratio.  Upper  part  shows  how  original 
parents  were  crossed  to  give  Fj  hybrid;  lower  part  shows  Fi  hybrid  producing 
four  kinds  of  gametes;  chance  matings  among  these  gametes,  when  Fi  is  inbred, 
result  as  indicated  in  the  large  set  of  squares  and  explains  the  9:3:3:1  ratio  in 
the  F2  generation.     {From  Coulter  atid  Coulter.) 

9  tall  wrinkled  yellow,  9  dwarf  smooth  yellow,  3  tall  wrinkled  green, 
3  dwarf  smooth  green,  3  dwarf  wrinkled  yellow,  i  dwarf  wrinkled 
green.  The  trihybrid  ratio  therefore  is  27:9:9:9:3:3:3:1.  This 
involves  64  individuals  and  8  phenotypes. 


MENDEL'S  LAWS  OF  HEREDITY  393 

ILLUSTRATIONS  OF  SIMPLE  MENDELIAN  INHERITANCE  IN 
BOTH  ANIMALS  AND  PLANTS^ 

J.    ARTHUR    THOMSON 

How  far  has  Mendel's  experience  been  confirmed? — There  has 
been  confirmatory  work  by  Correns  (on  peas,  maize,  and  garden- 
stock),  by  Tschermak  (on  peas),  by  De  Vries  (on  maize,  etc.),  by 
Bateson  and  his  collaborators  (on  a  large  variety  of  organisms),  by 
Darbishire  (on  mice),  by  Hurst  (on  rabbits),  by  Toyama  (on  silk- 
moths),  by  Davenport  (on  poultry),  and  so  on.  There  are  some 
difficulties  and  not  a  few  discrepancies,  but,  as  Bateson  says,  "  the 
truth  of  the  law  enunciated  by  Mendel  is  now  established  for  a  large 
number  of  cases  of  most  dissimilar  characters." 

In  experimenting  with  Lychnis,  Atropa,  and  Datura,  Bateson  and 
Saunders  found  that  the  phenomena  conformed  with  Mendel's  law 
"with  considerable  accuracy,  and  no  exceptions  that  do  not  appear  to 
be  merely  fortuitous  were  discovered.  In  the  case  of  Matthiola 
(garden-stock),  the  phenomena  are  much  more  complex.  There  are 
simple  cases  which  follow  Mendelian  principles,  but  others  of  various 
kinds  which  apparently  do  not.  The  latter  cases  fall  into  fairly  defin- 
ite groups,  but  their  nature  is  obscure." 

In  experiments  with  poultry,  the  phenomena  of  dominance  and 
recession  were  detected;  interbreeding  of  the  hybrid  offspring  resulted 
in  a  mixed  progeny,  "  some  presenting  the  dominant,  others  the  reces- 
sive character,  in  proportions  following  Mendel's  Law  with  fair  con- 
sistency, though  in  certain  cases  disturbing  factors  are  to  be  suspected." 

The  general  result,  so  far,  is  that  Mendel's  law  has  received  con- 
firmation in  a  number  of  very  dissimilar  cases. 

Dominant  and  recessive  characters. — Let  us  first  of  all  collect  a 
number  of  instances  of  contrasted  characters  which  behave  in  relation 
to  one  another  as  dominants  and  recessives. 

Dominant  Recessive 

Pisum  sativum Tallness  Dwarfness 

Round  seeds  Wrinkled  seeds 
Coloured  seed-coats  White  seed-coats 
Yellow  albumen  in  coty-  Green  albumen  in  coty- 
ledons ledons 
Purple  flowers  White  flowers 
Sweet  pea Tall  ordinary  form  Dwarf  or  "cupid"  vari- 
ety 

="  From  J.  Arthur  Thomson,  Heredity  (copyright  1907).  Used  by  special 
permission  of  the  publisher,  John  Murray,  London. 


394     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

Dominant  Recessive 

Stocks Coloured  WOiite 

Wheat  and  barley Beardless  Bearded 

Later  ripening  Rivett  Early  ripening  Polish 

wheat  wheat 

Non-immune  to  "rust"  Immune  to  "rust" 

Maize "Starch"  seed  "Sugar"  seed 

Nettles  (Urtica  pilulijera  and 

U.  dodartii) Serrate  leaf  margin  Entire  leaf  margin 

Mirabilis  jolapa  and  M,  rosea .  Rose  colour  Other  colours 

Mice Coloured  coat  Albino  coat 

Normal  "Waltzing"  variety 

Rabbits Coloured  coat  Albino  coat 

Angora  fur  Short  fur 

Poultry "Rose"    comb    of    Ham-  High  serrated  "single" 

burghs  and  Wyandottes        comb  of  Leghorns  and 

Andalusians 

Cattle Hornlessness  Horns 

Snails Bandless  shell  Banded  shell 

Other  instances  in  plants. — As  is  well  known,  there  are  two  almost 
equally  common  forms  of  wild  primrose:  (A)  thrum- types,  with 
short  styles  and  with  anthers  at  the  top  of  the  corolla-tube;  and  (B) 
pin-types,  with  long  styles  and  with  anthers  half  way  down  the  tube. 
The  thrum-type  is  dominant  over  the  pin-type. 

The  original  species  of  Chinese  primrose  {Primula  sinensis)  has  a 
palmate  leaf.  About  i860  a  sport  arose  (from  seed)  which  had  a 
pinnate  or  "fern"  leaf.  The  palmate  form  is  dominant,  and  the  fern 
leaf  is  recessive. 

The  deformed  "Snapdragon"  variety  of  sweet  pea  behaves  as  a 
recessive  to  the  normal  type. 

The  2 -row  barley  has  certain  lateral  flowers  which  are  exclusively 
staminate;  in  6-row  barley  all  the  flowers  are  staminate  and  pistillate, 
and  all  set  seed.  Mr.  Biffen  crossed  these  forms,  and  found  that  the 
more  negative  character  was  dominant.     The  offspring  were  2-rowed. 

Maize. — When  the  common  or  starchy  round-seeded  maize  is 
crossed  with  the  wrinkled-seeded  sugar-maize,  the  round  starchy  char- 
acter dominates.  When  an  egg-cell  of  the  wrinkled  sugar-maize  stock 
is  fertilised  by  a  pollen-cell  of  the  round  starchy  stock,  the  result  is  a 
round  seed  with  starchy  endosperm.  If  this  seed  is  sown,  it  becomes 
a  plant  which,  on  self-fertilisation,  forms  a  cob  with  a  mixture  of 
round  starchy  and  wrinkled  sugary  seeds  in  the  ratio  3:1.  The 
wrinkled  seeds  yield  sugar- maize;  the  round  seeds  yield  two  "impure 
rounds"  to  one  "pure  round."  Correns  has  observed  a  very  inter- 
esting case  in  which  two  pairs  of  contrasted  characters  are  imphcated. 


MENDEL'S  LAWS  OF  HEREDITY  395 

One  variety,  Zea  .mays  alba,  which  has  smooth  white  seeds,  was 
crossed  with  another  variety,  Zea  mays  coeruleodulcis,  which  has 
wrinkled  blue  seeds.  The  hybrids  (Fj)  had  smooth  blue  seeds,  one 
character  of  each  parent  being  dominant,  and  one  character  of  each 
parent  being  recessive.  The  hybrids  were  inbred,  and  the  progeny 
(F2)  showed  four  combinations — smooth  blue,  smooth  white,  wrinkled 
blue,  and  v/rinkled  white  (the  dominant  characters  are  italicised). 

In  the  next  generation  (F3),  the  wrinkled  white,  inbred,  yielded 
wrinkled  white — a  case  of  extracted  recessives,  breeding  true.  The 
smooth  whites  and  wrinkled  blues,  inbred,  yielded  partly  forms  like 
themselves  and  partly  wrinkled  white.  The  smooth  blues,  inbred, 
yielded  the  same  combinations  as  in  F3. 

A  finer  corroboration  of  Mendelian  could  hardly  be  wished. 

Nettles. — ^Correns  crossed  two  ''species  of  stinging-nettle,"  Urtica 
pilulifera  L.  and  U.  dodartii  L.,  which  resemble  one  another  except  as 
regards  leaf-margin,  strongly  dentate  in  the  former,  almost  entire  in 
the  latter.  The  hybrid  offspring  (Fi)  have  all  dentate  leaves  like  the 
male  or  the  female  parent,  as  the  case  may  be.  The  dentate  character 
is  absolutely  dominant.  The  inbred  (self-fertilised)  hybrids  produce 
offspring  (F2)  of  two  kinds,  with  dentate  and  with  entire  margins,  on  an 
average  in  the  Mendelian  proportion,  3:1. 

"Immunity  to  rust  in  wheat. — Some  kinds  of  wheat  are  very 
susceptible  to  the  fungoid  disease  known  as '  rust ' ;  others  are  immune. 
The  quality  of  immunity  to  rust  is  recessive  to  the  quality  of  predis- 
position to  rust. 

"When  an  immune  and  a  non-immune  strain  are  crossed  together 
the  resulting  hybrids  are  all  susceptible  to  '  rust.'  On  self-fertilisation 
such  hybrids  produce  seed  from  which  appear  dominant  'rusts'  and 
recessive  immune  plants  in  the  expected  ratio  of  3:1.  From  this 
simple  experiment  the  phrase  'resistance  to  disease'  has  acquired  a 
more  precise  significance,  and  the  wide  field  of  research  here  opened 
up  in  this  connection  promises  results  of  the  utmost  practical  as  well 
as  theoretical  importance.  To  the  question,  '  Who  can  bring  a  clean 
thing  out  of  an  unclean  ? '  we  are  beginning  to  find  an  answer,  nor  is 
the  answer  thie  same  as  that  once  given  by  Job"  (R.  C.  Punnett). 

Silkworms. — Toyama  paired  Siamese  silkmoths  with  yellow  or 
with  white  cocoons;  the  offspring  produced  only  yellow  cocoons. 
When  the  hybrids  were  inbred,  the  result  was  two  sets,  one  producing 
white  cocoons,  the  other  producing  yellow  cocoons,  and  the  proportion 
was  Mendelian — 25.037  white  and  74.96  yellow.     The  whites  bred 


396      READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

true;  the  yellows  when  inbred  showed  themselves  to  be  pure  domi- 
nants or  "yellows"  and  dominant-recessives — i.e.,  splitting  up  again 
into  yellows  and  whites  in  the  usual  proportion.  More  intricate 
experiments  confirmed  this  general  result. 

It  must  be  noted,  however,  that  Coutagne  has  made  much  more 
elaborate  experiments  with  different  results,  which  in  many  cases  can- 
not be  interpreted  on  the  Mendelian  theory.  Thus  he  found  (i)  that 
the  hybrid  forms  were  sometimes  blends  of  the  parents  and  different 
from  both;  (2)  that  in  other  cases  the  brood  included  some  like  one 
parent  in  a  particular  character,  some  Hke  the  other  parent,  and  some 
intermediate;  and  (3)  that  in  other  cases  the  individuals  showed  no 
fusion  of  characters,  but  resembled  one  or  other  parent.  It  is  likely 
that  the  discrepancy  may  be  explained  as  due  to  considerable  diversity 
of  origin  in  the  domesticated  races  of  silkworm,  so  that,  while  they 
breed  true  when  left  to  themselves,  a  disturbance  of  the  usual  routine 
leads  to  the  liberation  of  latent  characters. 

Lina  lapponica. — Miss  McCracken  has  made  a  fine  study  of  the 
hereditary  relations  in  this  Californian  beetle,  which  occurs  in  two 
types,  spotted  (dominant)  and  black  (recessive).  They  are  always 
crossing  in  natural  conditions,  but  there  are  no  intermediates,  and  it 
is  easy  by  isolation  to  rear  a  ''pure"  spotted  race  and  a  "pure"  black 
race.  When  spotted  forms  are  paired  they  may  produce  only  spotted 
progeny — a  case  of  extracted  dominants.  In  other  cases,  however, 
they  yield  spotted  and  black  forms  (1,021  spotted,  345  black),  i.e.,  in 
the  Mendelian  proportion  of  3 :  i — a  case  of  dominant-recessives  inbred. 

Snails. — Lang  paired  "pure"  five-banded  forms  of  the  common 
or  garden  snail.  Helix  hortensis,  with  bandless  forms  from  bandless 
colonies.  The  young  of  the  first  generation  were  all  bandless,  the 
banded  character  being  recessive.  When  these  were  paired  the  off- 
spring were  bandless  and  banded  in  the  Mendelian  ratio,  3:1.  Fur- 
ther experiments  confirmed  this,  not  only  as  regards  bands,  but  also 
as  regards  colour  (yellow  or  red),  size,  and  the  form  of  the  umbilicus. 
//  may  be  said,  therefore,  that  common  snails  {Helix  hortensis  and  Helix 
nemoralis)  illustrate  Mendelian  inheritance. 

Poultry. — Numerous  breeding  experiments  with  poultry  have 
been  made  by  Bateson,  Bateson  and  Punnett,  Hurst,  Davenport,  and 
others,  many  of  which  show  Mendelian  phenomena  with  great  clear- 
ness, while  others  are  strangely  conflicting.  One  of  the  reasons  for  the 
complicated  results  is  evidently  to  be  found  in  the  difficulty  of  securing 
thoroughly  "pure"  breeds,  for  many  that  breed  true  as  long  as  they 


MENDEL'S  LAWS  OF  HEREDITY  397 

are  inbred  tend  to  liberate  latent  characters  when  the  ordinary  course 
of  breeding  is  departed  from. 

Hurst  contrasts  the  following  characters,  which  usually  show  them- 
selves dominants  and  recessives;  but  it  has  to  be  admitted  that  the 
dominance — always  complete  for  some  characters — is  for  others  fre- 
quently, or  even  always  incomplete — i.e.,  showing  traces  of  the  corre- 
sponding recessives. 

Dominant  Characters  Recessive  Characters 

Rose  comb  Leaf  comb,  single  comb 

White  plumage  Black  plumage,  buff  plumage 

Extra  toes  Normal  toes 

Feathered  shanks  Bare  shanks 

Crested  head  Uncrested  head 

Brown  eggs  White  eggs 

Broodiness  Non-broodiness 

Davenport's  copiously  illustrated  work  is  also  of  great  interest. 
He  shows  in  case  after  case  that  the  character  dominant  in  the  first 
hybrids  is  more  or  less  influenced  by  the  recessive  character.  Polish 
fowls  with  a  large  hernia  of  the  brain  on  the  top  of  the  head  were 
paired  with  Minorcas  with  normal  heads.  The  hybrids  showed  no 
hernia,  but  most  of  them  showed  a  frontal  prominence.  When  the 
hybrids  were  inbred  the  hernia  occurred  in  23.5  per  cent — a  close 
approximation  to  the  theoretical  25  per  cent. 

Single-combed  black  Minorcas  were  crossed  with  white-crested 
black  Polish  fowls  with  a  very  small  bifid  comb.  The  hybrids  had 
combs  single  in  front,  split  behind.  When  the  hybrids  were  inbred 
there  resulted  in  a  total  of  loi  offspring,  29.7  per  cent  with  single 
combs  (like  Minorcas),  46.5  per  cent  with  Y-shaped  combs,  and  23.8 
per  cent  with  no  combs  or  only  papillae  (like  the  Polish  forms).  Here, 
again,  the  result  is  in  a  general  way  Mendelian,  but  the  Y-like  comb 
is  a  complication. 

Pigeons. — R.  Staples-Browne  crossed  a  web-footed  pigeon  (an 
occasional  discontinuous  variation)  with  a  normal  form,  and  got  six 
normal  young.  In  other  words,  the  web-foot  character  is  recessive 
to  the  normal  foot  character.  The  hybrids  were  inbred,  and  in  one 
case  produced  nine  with  normal  feet  and  three  with  webbed-feet — a 
Mendehan  splitting-up.  But  from  another  pair  of  hybrids  seventeen 
normal  offspring  resulted.  Thus,  the  illustration  of  Mendelian 
inheritance  is  inconclusive.     Besides  the  numbers  were  too  small. 

We  have  noticed  elsewhere  that  crossing  different  breeds  of  pigeons 
often  results  in  forms  which  more  or  less  resemble  the  reputed  original 


398     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

ancestor,  the  wild  rock  dove;  in  other  words,  reversions  occur.  Often, 
however,  the  results  seem  quite  anomalous,  which  is  probably  due  to 
the  number  of  latent  characters  which  different  races  of  pigeons  appear 
to  carry. 

Mice. — Mendelian  phenomena  have  been  carefully  studied  in 
mice.  Thus,  when  a  grey  mouse  is  paired  with  an  albino,  the  hybrid 
offspring  are  always  grey.  When  these  are  inbred,  they  yield  greys 
and  albinos,  approximately  in  the  proportion  of  3:1.  Thus  Cuenot 
obtained  198  grey,  and  72  albinos. 

Darbishire  has  obtained  many  results  which  harmonise  well  with 
Mendelian  theory,  while  others  require  some  ingenuity  if  they  are  to 
be  fitted  in  with  this  interpretation.  As  a  good  case  we  may  cite  one 
where  the  inbreeding  of  pigmented  mice — derived  from  crossing  pig- 
mented and  albino  individuals — yielded  159  pigmented  young  and  55 
albinos  (53.5  being  the  theoretical  anticipation).  When  similar 
hybrids  were  paired  with  pure  albinos,  they  yielded  69  pigmented  and 
69  albino  forms,  precisely  as  the  theory  would  lead  us  to  expect: 

D  R 

\. 

D(R) 

X 
D(R) 


I  D+2  D(R)  +  i  R 

X 

2  R 


D(R)  R 


Cuenot  crossed  an  albino  AG  (with  latent  grey)  with  an  albino  AB 
(with  latent  black),  and  obtained  albinos  (AGAB).  He  crossed  a 
black  mouse  CB  with  an  albino  AY  (with  latent  yellow),  and  obtained 
yellow  mice  (CBAY).  He  then  paired  AGAB  (albino)  with  CBAY 
(yellow)  and  obtained  151  young — 81  albinos,  34  yellow,  20  black,  16 
grey;  the  theoretical  anticipation  being  — 76  albinos,  38  yellow,  19 
black,  19  grey.  This  is  an  exceedingly  striking  and  convincing  case. 
Waltzing  mice. — The  mice  of  this  interesting  Japanese  breed  have 
among  other  peculiarities  the  habit  of  waltzing  round  in  circles.  When 
waltzing  mice  are  crossed  with  normal  mice,  their  abnormal  quality 
behaves  as  a  recessive. 


MEN'DEL'S  LAWS  OF  HEREDITY  399 

Guinea-pigs. — If  a  black  guinea-pig  of  pure  race  be  crossed  with 
a  white  one  the  offspring  will  be  all  white,  and  if  these  are  mated  with 
each  other  the  recessive  white  character  reappears  on  the  average  in 
one  in  four  of  their  offspring.  These  whites  mated  with  each  other 
produce  only  white  offspring,  while  the  black  are  as  usual  of  two  kinds, 
pure  blacks  and  impure  blacks.  Similarly,  as  Professor  Castle  has 
shown,  a  rough  coat  is  dominant  over  a  smooth  coat,  and  a  short  coat 
over  a  long  coat. 

Rabbits. — Hurst  paired  white  Angora  rabbits  (with  pink  eyes  and 
silky  hair)  with  "Belgian  hare"  rabbits  (with  pigmented  skin,  dark 
eyes,  and  short  yellow  fur).  The  hybrids  were  pigmented  like  the 
"  Belgian  hares,"  but  the  fur  was  grey  like  that  of  the  wild  rabbit. 
These  hybrids  were  inbred,  and  14  distinct  types  resulted — an  apparent 
''epidemic  of  variation"  to  which  Mendel's  theory  has  supplied  the 
clue,  for  four  pairs  of  contrasted  characters  are  involved  in  the  hybrid 
inbreeding — namely,  short  hair  versus  long  hair,  pigmented  coat  versus 
albinos,  grey  versus  black  coat,  uniform  versus  marked  coat  (Dutch 
marking  latent  in  the  albinos),  and  the  14  distinct  types  illustrate  the 
possible  combinations. 

As  regards  short  hair  versus  long  hair,  Hurst  found  that  when  the 
short-coated  hybrids  were  inbred  they  produced  short-haired  forms 
like  the  Belgian  hare  grandparent,  and  long-haired  forms  Hke  the 
Angora  grandparent.  Out  of  70  which  reached  the  age  of  two  months 
or  more,  53  were  short-haired  and  17  long-haired — a  close  approxi- 
mation to  the  Mendelian  anticipation,  52.5  :  17.5.  Similarly,  as 
regards  pigmented  coat  versus  albino,  the  hybrids,  when  inbred, 
yielded  132  pigmented  and  39  albino  forms — a  close  approximation  to 
the  Mendelian  expectation,  129  :  43;  and  so  on. 

Cats. — There  are  some  interesting  results  as  to  colour  (Doncaster). 
Thus,  ''pure"  orange  ?  crossed  by  "pure"  black  6  gives  tortoiseshell 
females  and  yellow  males,  but  black  crossed  by  orange  gives  black 
males  or  females,  tortoiseshell  females,  and  orange  males.  It  seems 
that  orange  usually  dominates  over  black  in  males,  while  in  females 
the  orange  (for  some  unknown  reason)  is  less  dominant  and  tortoise- 
shell  results.  Male  tortoiseshell  cats  are  very  rare.  In  this  case  the 
results  are  complicated  by  some  peculiarity  wrapped  up  with  "sex." 

When  a  male  tortoiseshell  is  paired  with  a  female  tortoiseshell  the 
kittens  are  tortoiseshell,  orange,  and  black — which  is  what  Mendelian 
theory  would  lead  us  to  expect. 

Man. — Evidence  of  Mendelian  phenomena  in  man  is  as  yet  very 
scanty.     It  appears  that  the  condition  known  as  brachydactylism, 


4oo     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

where  the  fingers  are  all  thumbs  with  two  joints  instead  of  three, 
is  dominant  over  the  normal.  In  five  generations  chronicled  by  Fara- 
bee  about  half  of  the  offspring  were  of  the  abnormal  type,  though  the 
marriages  were  apparently  always  with  unrelated  normal  individuals. 
Moreover,  no  normal  member  of  the  lineage  is  known  to  have  trans- 
mitted the  abnormality.  Another  good  case  has  been  recently  dis- 
cussed by  Drinkwater. 

Of  great  interest  also  is  Mr.  Nettleship's  account  of  the  descend- 
ants of  one  Jean  Nougaret  (born  1637),  who  was  afflicted  with  "night- 
blindness" — a  condition  apparently  due  to  loss  of  visual  purple.  It 
seems  to  behave  like  a  unit  character.  There  are  records  of  over  2,000 
individuals;  and  the  night-blindness  is  dominant  over  normal  eye- 
sight. The  notable  point  is  that  during  two  and  a  half  centuries  no 
normal  member  of  the  lineage  who  married  another  normal,  whether 
related  or  not,  ever  transmitted  the  disease. 

Human  eye-colour  affords  another  illustration.  It  is  largely 
determined  by  the  presence  or  absence  of  two  distinct  layers  of  pig- 
ment. In  the  true  blue  eye  only  one  of  these  pigmentary  layers  is 
visibly  present,  the  posterior  purple  pigment  of  the  choroid,  which, 
being  reflected  through  the  fibrous  structure  of  the  iris,  produces  the 
blue  colour.  In  the  absence  or  partial  absence  of  this  pigment  the 
eye  appears  to  be  "pink,"  as  in  albinos.  In  the  ordinary  brown  eye 
two  layers  of  pigment  are  present,  for  in  addition  to  the  posterior 
purple  layer  there  is  also  an  anterior  brown  layer,  in  front  of  the  iris. 
Major  C.  C.  Hurst  found  that  the  eye  with  two  layers  of  visible  pigment 
(duplex)  is  dominant  and  the  eye  with  one  layer  of  visible  pigment 
(simplex)  recessive.  Or,  putting  it  in  another  way,  the  presence  of  the 
brown  front  layer  is  dominant  to  its  absence.  Practically  the  same  con- 
clusion was  reached  independently  by  Professor  and  Mrs.  Davenport. 

The  Davenports  and  Major  Hurst  have  also  brought  forward  some 
evidence  illustrating  in  typical  Caucasians  the  dominance  of  dark  to 
fair  skins,  their  segregation  in  the  same  family,  and  the  apparent 
purity  of  the  extracted  fair  individuals.  Hurst  also  gives  evidence 
that  "fiery  red"  hair  behaves  as  a  recessive  to  brown,  and  that  the 
musical  sense  or  temperament  is  also  recessive.  It  seems  as  if  an 
individual  is  non-musical  owing  to  the  presence  of  an  inhibitory  factor 
preventing  the  expression  of  musical  temperament  which  is  poten- 
tially present  in  everyone  (Hurst,  19 12). 

It  would  be  interesting  to  have  precise  information  as  to  the  pro- 
geny of  Eurasians  who  intermarry,  for  here  the  original  hybrids  result 
from  the  mixture  of  two  very  distinct  races. 


CHAPTER  XXVIII 
THE  PHYSICAL  BASIS  OF  MENDELISM^ 

ERNEST  B.  BABCOCK  AND  ROY  E.  CLAUSEN 

Recent  investigations  in  heredity  have  focused  attention  upon  the 
chromosome  mechanism  as  the  physical  basis  for  the  segregation  and 
recombination  of  the  units  of  Mendehan  inheritance.  The  importance 
of  cytological  phenomena  to  students  of  genetics  is  admirably  summed 
up  by  E.  B.  Wilson  in  the  brief  statement  that  "heredity  is  a  conse- 
quence of  the  genetic  continuity  of  cells  by  division,  and  the  germ  cells 
form  the  vehicle  of  transmission  from  one  generation  to  another."  It 
is  appropriate,  therefore,  to  introduce  the  subject  of  Mendelism  with  a 
formal  and  brief  treatment  of  the  chromosome  mechanism  and  its 
mode  of  operation,  on  the  one  hand,  in  the  building  up  of  the  body 
from  the  single  cell  with  which  the  individual  begins  its  existence,  and, 
on  the  other  hand,  in  the  production  of  germ  cells  when  the  individual 
reaches  the  reproductive  period  of  its  life  cycle.  It  is  the  purpose  of 
this  chapter  merely  to  deal  with  the  fundamental  facts  of  cytology 
which  are  necessary  to  an  understanding  of  the  connection  between 
cell  behavior  and  Mendelian  phenomena.  Details  unessential  to  such 
an  understanding,  however  well  established  cytologically,  will  not  be 
dealt  with  in  this  treatment  to  the  end  that  the  cardinal  points  may  be 
presented  as  simply  and  as  clearly  as  possible. 

The  chromosomes. — ^With  few  exceptions  the  number  of  chromo- 
somes in  the  cells  of  any  individual  is  constant  and  characteristic  of 
the  species  to  which  the  individual  belongs.  Thus  it  is  characteristic 
of  Drosophila  ampelophila  that  the  cells  contain  eight  chromosomes. 
In  maize  the  cells  contain  twenty  chromosomes,  in  wheat  sixteen,  and 
in  man  forty-eight,  and  so  on  through  the  entire  plant  and  animal 
kingdoms. 

Not  only  is  the  number  of  chromosomes  in  a  particular  species 
constant,  but  the  chromosomes  themselves  possess  a  definite  indi- 
viduality. Man  and  tobacco  have  cells  with  the  same  number  of 
chromosomes.     It  is  needless  to  point  out  that  these  chromosomes, 

^  From  E.  B.  Babcock  and  R.  E.  Clausen,  Genetics  in  Relation  to  Agriculture 
(copyright  1918).  Used  by  special  permission  of  the  publishers,  The  McGraw- 
Hill  Book  Company. 

401 


402      READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

however,  are  qualitatively  very  different.  Similarly  within  the  species 
the  chromosomes  are  not  all  alike;  on  the  contrary,  especially  in 
certain  forms,  they  exhibit  very  marked  differences  in  size  and  shape. 
This  is  peculiarly  well  illustrated  in  Drosophila  as  shown  in  Fig.  70. 
Here  it  is  possible  to  recognize  in  the  female  two  large  pairs  of  curved 
chromosomes  very  similar  in  size  and  shape.  There  is  also  a  very  small 
pair  of  chromosomes,  and  finally  there  is  a  pair  of  straight  ones  about 
two-thirds  as  long  as  the  large  curved  chromosomes.  In  the  male  the 
same  relations  hold  except  that  instead  of  the  pair  of  straight  chromo- 
somes there  is  a  pair  consisting  of  one  straight  and  one  somewhat 
larger  hooked  chromosome.  The  significance  of  this  difference  in 
chromosome  content  in  the  sexes  will  be  pointed  out  in  a  consideration 


FEMALE  HALE 


Fig.  70. — Diagram  showing  the  characteristic  pairing,  size  relations,  and 
shapes  of  the  chromosomes  of  Drosophila  ampelophila.  In  the  male  an  X  and  a 
Y  chromosome  correspond  to  the  X  pair  of  the  female.  On  the  basis  of  X  100 
the  length  of  each  long  autosome  159,  of  each  small  autosome  12,  and  of  P'  112,  of 
the  long  arm  of  F  71,  and  of  the  short  arm  of  F  41.  {From  Bahcock  and  Clausen, 
after  Bridges.) 

of  the  inheritance  of  sex.  The  pair  of  straight  chromosomes  we  call 
the  sex  or  X-chromosomes,  the  unequal  mate  of  the  X-chromosome  in 
the  male  of  this  species  is  called  the  Y-chromosome.  The  other 
chromosomes  are  called  autosomes  when  it  is  desired  to  distinguish 
them  as  a  class  from  the  sex  chromosomes.  Drosophila  is  not  unique 
in  possessing  chromosomes  of  such  characteristic  shapes  and  sizes;  but 
more  and  more  as  cytology  advances  it  is  becoming  possible  to  dis- 
tinguish chromosomes,  and  to  recognize  them  a,t  every  cell  division. 
Moreover;  the  characteristic  paired  relations  which  exist  among 
the  chromosomes  of  Drosophila  are  of  general  significance.  When 
mature  germ  cells  are  formed  in  an  individual,  reduction  divisions 
occur  by  means  of  which  the  chromosome  number  is  reduced  in  the 
germ  cells  to  one-half  that  characteristic  of  the  body  cells.     Thus  the 


THE  PHYSICAL  BASIS  OF  MENDELISM  403 

germ  cells  of  Drosophila  contain  four  chromosomes  as  the  result  of  a 
reduction  which  takes  place  in  such  a  manner  that  each  germ  cell  con- 
tains one  member  of  each  pair  of  chromosomes.  As  a  consequence, 
the  germ  cell  of  Drosophila  contains  two  large  curved  autosomes, 
representing  the  two  pairs  of  these  chromosomes,  one  small  autosome, 
and  one  X-  or  one  Y-chromosome.  The  same  thing  is  true  for  other 
species  of  plants  and  animals — in  the  reduction  divisions  the 
chromosomes  are  distributed  in  such  a  manner  that  each  germ  cell 
receives  one  member  of  each  pair  of  chromosomes.  It  follows  from 
this  that  in  general  a  definite  number  of  pairs  of  chromosomes  is 
characteristic  of  the  body  cells  of  individuals  of  a  given  species,  and, 
taking  the  chromosomes  by  pairs,  one  member  of  each  pair  is  derived 
from  one  parent  and  the  other  from  the  other  parent. 

From  the  standpoint  of  interpretation  the  chromosomes  are  aggre- 
gates of  chromatin  material  which  in  itself  is  definitely  and  highly 
organized.  Our  conceptions  of  this  feature  of  cell  organization  are 
based  on  appearances  of  the  cytological  preparations  from  certain  of 
the  more  favorable  plants  and  animals  and  further  interpreted  by 
investigations  on  heredity.  Accordingly  the  entire  chromatin  con- 
tent of  the  nucleus  is  regarded  as  made  up  of  a  definite  number  of  indi- 
vidual chromatin  elements  called  chromomeres.  The  number  of 
chromomeres  in  a  cell  of  any  species  must  run  into  the  thousands.  A 
certain  definite  group  of  these  elements  make  up  each  chromosome, 
and  at  every  cell  division  this  chromosome  is  reformed  from  the  same 
group  of  chromomeres,  but  the  chromosome  is  definitely  organized 
with  respect  to  the  position  or  locus  occupied  by  each  chromomere. 
At  certain  stages  in  the  history  of  chromosomes,  they  are  simply  lines 
of  chromomeres,  very  much  like  single  strings  of  beads  with  each  bead 
corresponding  to  a  chromomere.  Now  it  appears  probable  that  all 
the  chromomeres  in  a  chromosome  are  different,  as  though  our  string 
of  beads  had  no  duplicates  throughout  its  length.  Moreover,  each 
chromomere  has  a  definite  place  or  locus  in  the  particular  chromosome 
in  which  it  belongs  and  it  is  always  found  at  that  particular  locus. 
The  chromomeres  of  this  discussion  are  identified  with  the  factors  of 
Mendelian  heredity,  and  how  closely  this  conception  of  the  nature  of 
chromatin  and  its  complex  organization  corresponds  to  the  modern 
view  of  Mendelian  phenomena  will  be  pointed  out  as  each  new  phase 
of  Mendelism  is  taken  up. 

Somatic  cell  division. — The  phenomena  of  cell  division  (called 
mitosis)  are  represented  in  outline  in  Fig.  71,  for  a  species  having  four 


404     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

chromosomes  in  its  body  cell.  Bearing  in  mind  the  description  which 
has  just  been  given  of  the  organization  of  the  chromatin  material  we 
may  follow  the  steps  involved  in  mitosis  as  they  are  outlined  in  this 
figure.  In  the  "  resting  "  cell  at  A  the  chromatin  is  scattered  through- 
out the  nucleus  in  clumps  or  knots  loosely  strung  together  to  form  an 
irregular  network.  As  the  cell  prepares  for  division  the  chromatin 
elements  appear  in  more  definite  form  until  at  B  the  chromomeres  have 


Fig.  71. — Diagram  of  mitosis  in  a  species  having  four  chromosomes  in  its 
cells.  ^,  the  "resting"  cell;  5,  formation  of  the  spireme  thread;  C,  longitudinal 
division  of  the  spireme  thread  and  transverse  segmentation  into  four  chromosomes; 
D,  separation  of  the  daughter  chromosomes  formed  by  longitudinal  splitting 
of  spireme  thread;  E,  beginnings  of  nuclear  reconstruction  and  division  of  the  cell 
body;  F,  cell  division  complete  and  daughter  nuclei  in  the  "resting"  stage. 
{From  Babcock  and  Clausen.) 


arranged  themselves  in  a  single  row  in  a  long  continuous  spireme- 
thread.  This  spireme-thread  may  be  considered  to  be  made  up  of  the 
four  chromosomes  united  end  to  end  with  the  chromomeres  arranged 
in  a  linear  series.  As  mitosis  progresses  to  the  next  stage  represented 
at  C,  each  chromomere  of  the  spireme-thread  divides  into  two,  so  that 
a  double  spireme-thread  results  from  the  longitudinal  splitting  of  the 
original  thread.  Both  parts  of  the  thread  are  quantitatively  and  quali- 
tatively equal,  for,  by  the  splitting  of  all  the  chromomeres  both  of  the 


THE  PHYSICAL  BASIS  OF  MENDELISM  405 

threads  come  to  possess  all  of  the  individual  elements  of  the  original 
spireme  thread.  Following  the  splitting  of  the  chromomeres  and  the 
formation  of  a  double  spireme,  the  spireme-thread  contracts  and  seg- 
ments transversely  forming  four  double  chromosomes,  the  number 
characteristic  of  the  cells  of  this  individual.  This  is  the  stage  shown 
at  C  where  also  is  shown  the  origin  of  the  spindle,  a  part  of  the  mechan- 
ism in  mitosis.  The  chromosomes  now  still  further  contract  until 
they  assume  their  characteristic  shapes  and  sizes.  They  next  appear 
in  an  equatorial  position  on  the  spindle  as  shown  at  D,  where  the  two 
pairs  of  double  chromosomes,  one  larger  and  one  smaller,  are  dia- 
grammed and  the  nucleolus,  the  large  black  body  of  the  previous  steps, 
is  shown  cast  out  and  degenerating.  The  daughter  chromosomes  of 
each  pair  now  separate  from  each  other  until  at  E  they  have  moved 
nearly  to  the  opposite  poles  of  the  spindles  and  are  beginning  to  fray 
out  and  seemingly  to  lose  their  identity.  At  this  stage  actual  division 
of  the  cell  body  has  begun.  Finally  at  F,  the  chromosomes  have  com- 
pletely lost  all  appearance  of  their  identity,  the  chromatin  material 
is  distributed  thruout  the  nucleus  as  in  the  original  cell  shown  at  A , 
and  the  nucleolus  has  been  reformed  in  each  nucleus.  Division  of  the 
cell-body  has  resulted  in  two  daughter  cells,  each  of  which,  so  far  as 
chromomeres  are  concerned,  contains  exactly  the  same  chromatin 
elements  as  the  original  cell. 

There  are  many  variations  in  this  process  particularly  in  the  order 
of  occurrence  of  the  steps,  but  these  variations  in  nowise  modify  the 
essential  fact  of  mitosis  which  is  that  the  chromatin  material  of  the 
cell  is  converted  into  a  thread  which  splits  thruout  its  entire  length 
into  two  halves  so  that  the  daughter  nuclei  receive  exactly  equivalent 
portions  of  chromatin  material.  This  precise  division  of  the  chro- 
matin is  brought  about  by  a  division  of  each  chromomere  so  that  not 
only  do  the  daughter  nuclei  receive  equivalent  portions  of  chromatin 
but  these  portions  are  also  equivalent  qualitatively  to  the  entire 
chromatin  content  of  the  mother  cell.  By  this  method  then  each  of 
the  cells  of  the  body  finally  comes  to  possess  not  only  the  whole  num- 
ber of  chromosomes  contributed  by  the  two  parents,  but  also  the 
entire  set  of  chromatin  elements  which  it  received  from  them.  The 
extreme  care  with  which  the  cell  mechanism  partitions  the  chromatin 
material  in  each  successive  cell  division  is  in  itself  eloquent  testimony 
of  the  fundamental  importance  of  this  material. 

The  production  of  germ  cells. — In  the  production  of  germ  cells  a 
different  set  of  phenomena  occur  which  result  in  a  reduction  of  this 


4o6     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

number  of  chromosomes  to  one-half  that  characteristic  of  the  somatic 
cells.  Preceding  the  actual  reduction  division  the  chromatin  passes 
through  a  complex  series  of  steps  which  may  be  included  under  the 
term  synapsis.  (This  term  is  sometimes  applied  in  a  specific  sense 
to  the  pairing  of  homologous  chromosomes  and  sometimes  to  the  con- 
traction of  the  chromatin  threads  in  the  conjugation  stage.)  The 
essential  steps  in  the  prereduction  process  are  shown  in  outline  in 
Fig.  72.    At  y4  is  diagrammed  a  "  resting  "  nucleus  at  the  completion  of 


Fig.  72. — The  reduction  division  as  represented  for  a  species  whose  diploid 
number  is  four.  A,  "resting"  nucleus  of  a  primary  germ  cell;  B,  formation  of 
paired  threads  of  chromomeres;  C,  conjugation  of  homologous  chromosomes 
(synapsis) ;  D,  loosening  of  the  synaptic  knots;  E,  condensation  of  the  chromosomes 
and  disappearance  of  the  nuclear  membrane;  F,  homologous  chromosomes  about 
to  pass  to  opposite  poles,  thus  giving  each  secondary  germ  cell  a  member  of  each 
pair  and  one-half  the  somatic  number.     {From  Babcock  and  Clausen.) 


the  multiplication  divisions  in  the  germ  plasm.  As  a  result  of  the  exact 
type  of  mitosis  which  has  been  outlined  above  it  contains  the  full  num- 
ber of  chromosomes  characteristic  of  the  species.  The  chromatin  of 
the  nucleus  next  becomes  organized  into  threads  of  chromomeres 
which  pair  as  shown  at  B.  In  this  diagram  the  paired  threads  are 
taken  to  represent  homologous  chromosomes,  and  the  opposite  chro- 
momeres of  the  two  chromosomes.     The  paired  threads  contract  and 


THE  PHYSICAL  BASIS  OF  MENDELISM  407 

fuse  along  their  entire  length  giving  the  figure  diagrammed  at  C  in 
which  the  two  loops  represent  two  pairs  of  homologous  chromosomes 
in  the  conjugation  stage,  the  essential  step  in  synapsis.  Following 
this  stage  the  two  contracted  loops  of  chromatin  split  lengthwise  and 
unravel  in  somewhat  the  manner  shown  in  D.  These  filaments  con- 
tract again  forming  the  intertwined  pairs  of  chromosomes  shown  at  E, 
and  the  nuclear  membrane  thereupon  begins  to  disappear.  Further 
contraction  and  the  formation  of  a  spindle  results  in  the  reduction 
figure  at  F,  the  significant  feature  of  which  is  the  fact  that  each  of  the 
daughter  nuclei  resulting  from  this  division  receives  only  two  chromo- 
somes instead  of  the  four  which  the  original  cell  at  A  contained.  Since 
the  original  cell  contained  one  pair  of  larger  and  one  pair  of  smaller 
chromosomes,  the  daughter  cells  which  are  formed  each  receive  one 
larger  and  one  smaller  chromosome. 

Cytological  investigation  is  not  yet  in  agreement  as  to  the  inter- 
pretation of  synapsis  especially  as  to  the  manner  in  which  the  phe- 
nomena therein  concerned  are  connected  with  preceding  mitotic  divi- 
sions. Considering  certain  cytological  investigations  and  the  results 
of  research  in  heredity  together,  it  appears  that  the  threads  which  pair 
in  stage  B  represent  pairs  of  chromosomes  with  homologous  chromo- 
meres  occupying  corresponding  positions  along  their  entire  length. 
Likewise  the  contraction  stage  at  C  is  taken  to  represent  a  conjugation 
of  the  members  of  pairs  of  chromosomes  which  later  again  separate. 
Other  cytological  evidence  indicates  that  in  some  forms  the  conjuga- 
tion of  pairs  of  homologous  chromosomes  is  brought  about  in  another 
way.  However,  the  essential  fact  is  the  same  in  either  case.  In  the 
reduction  figure  the  members  of  each  pair  of  chromosomes  are  dis- 
tributed to  the  opposite  poles  of  the  spindle  so  that  the  daughter 
nuclei  received  only  one  member  of  each  pair. 

The  significance  of  synapsis  lies  in  the  conjugation  of  homologous 
chromosomes.  In  the  mitoses  which  have  preceded  this  particular 
division,  the  chromosomes  were  each  time  conceived  to  be  reformed 
from  the  identical  group  of  chromomeres  which  they  contained  origi- 
nally". In  synapsis,  however,  as  shown  at  B  there  is  a  certain  amount 
of  intertwining  of  the  paired  threads  and  in  the  unraveling  of  the 
chromosomes  after  the  contraction  stage  there  is  likewise  a  twisting 
of  the  filaments  about  each  other.  The  indications  are,  therefore, 
that  in  synapsis  there  is  a  possibility  of  interchange  of  chromatin 
material  between  the  members  of  a  pair  of  homologous  chromosomes. 
In  all  cases,  however,  in  order  to  uphold  our  conception  of  the  definite 


4o8     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 


pair  of  chromosomes.     {From  Babcock  and 
Clausen,  after  Muller.) 


organization  of  the  chromosomes  with  respect  to  the  chromomeres 
which  they  contain,  this  interchange  of  material  must  involve  exactly 
equivalent  portions  of  the  two  chromosomes.     The  chromosomes  of 

the  reduction  division  shown  at 
F  may  not,  therefore,  be  identi- 
cal with  the  four  originally 
present  in  A ,  but  may  represent 
various  combinations  of  portions 
of  both  members  of  a  particular 
pair  of  chromosomes.  The  re- 
sults of  such  interchange  between 
Fig.  73.— Diagram  of  chromatin  inter-  members  of  homologous  pairs  of 
change  between  homologous  members  of  a     chromosomes  is  shown  in  Fig.  73 . 

At  the  left  is  shown  a  pair  of 
chromosomes,  one  in  outline,  the 
other  in  full  black.  In  the  middle  the  steps  in  chromatin  interchange 
are  diagrammed  and  finally  at  the  right  this  interchange  results  in 
a  pair  of  chromosomes  each  of  which  is  made  up  of  parts  of  both 
members  of  the  original  pair  of  chromosomes.  Various  combinations 
may  result  depending  on  the  points  at  which  interchange  takes  place, 
but  in  every  case  the  exchange  involves  corresponding  portions  of 
the  two  chromosomes. 

Independent  distribution  of  chromosomes. — In  Fig.  74  are  illus- 
trated diagrammatically  the  chromosomes  of  Drosophila,  with  particu- 
lar reference  to  their  size  and  form  relations  and  to  their  character- 
istic pairing  in  the  cell.  One  member  of  each  of  these  pairs  of  chro- 
mosomes was  contributed  by  the  female  parent  and  one  member  by 
the  male  parent.  In  the  reduction  divisions  these  chromosomes  are 
separated  so  that  each  germ  cell  contains  one  member  of  each  pair  of 
chromosomes.  The  simplest  condition  which  could  obtain  is  that  of 
independent  distribution  in  each  pair  of  chromosomes  such  that  the 
particular  member  of  one  pair  which  went  to  a  given  pole  of  the  reduc- 
tion spindle  would  have  no  influence  on  the  distribution  of  the  mem- 
bers of  any  other  pair.  Such  independent  distribution  of  chromo- 
somes appears  to  be  actually  the  type  followed  in  reduction.  As  a 
consequence  the  germ  cells  contain  various  combinations  of  chromo- 
somes with  respect  to  their  original  parental  derivation.  In  Fig.  74 
the  types  of  combinations  of  maternal  and  paternal  chromosomes  and 
their  mode  of  derivation  in  Drosophila  are  shown  diagrammatically. 
Two  germ  cells,  one  from  the  female  with  the  chromosomes  in  outline, 


THE  PHYSICAL  BASIS  OF  MENDELISM 


409 


and  the  other  from  the  male  with  the  chromosomes  in  full  black,  unite 
to  form  the  female  zygote  shown  in  the  middle  of  the  figure.  The 
combinations  of  maternal  and  paternal  chromosomes  which  result  in 
the  production  of  germ  cells  in  such  an  individual  are  shown  diagram- 


FiG.  74. — Diagram    showing    consequences    of    independent   segregation   of 
chromosomes  in  Drosophila  ampelophila.     {From  Babcock  and  Clausen.) 

matically  in  the  lower  portion  of  the  figure.  There  are  eight  different 
ways  in  which  the  chromosomes  may  be  grouped  in  the  reduction 
figures  and  on  the  basis  of  chance  any  one  of  these  types  is  as  likely 
to  occur  as  any  other.  As  a  result  there  are  sixteen  possible  combi- 
nations of  chromosomes  in  the  germ  cells  with  respect  to  the  original 


4IO     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

derivation  of  the  chromosomes,  whether  from  the  female  or  from  the 
male  parent.  This  of  course  represents  only  the  total  number  of 
possible  combinations  of  entire  chromosomes.  By  exchange  of 
chromatin  material  between  homologous  chromosomes  resulting  in  the 
formation  of  combination-chromosomes  the  number  of  actual  com- 
binations is  greatly  increased. 

The  number  of  chromosome  combinations  resulting  from  inde- 
pendent distribution  is  that  number  possible  when  each  pair  of  chro- 
mosomes is  considered  separately,  and  every  combination  has  an  equal 
chance  of  occurrence.  With  a  form  having  but  two  pairs  of  chromo- 
somes there  would  be  only  four  possible  combinations,  three  pairs 
would  give  eight,  four  pairs  sixteen,  and  in  general  the  number  of 
possible  combinations  is  given  by  the  expression  2"  in  which  n  is  the 
number  of  pairs  of  chromosomes  in  the  individual  in  question.  In 
tobacco  which  has  24  pairs  of  chromosomes  the  number  of  possible 
combinations  in  the  germ  cells  reaches  the  enormous  total  of  16,777,- 
216.  This  means  that  in  the  formation  of  zygotes  in  a  self-fertilized 
tobacco  plant  the  actual  parental  combinations,  i.e.,  combinations 
identical  with  those  of  the  germ  cells  which  united  to  form  the  indi- 
vidual in  question,  occur  only  twice  in  over  sixteen  million  times,  and 
this  proportion  is  still  further  lessened  when  the  interchange  of  chro- 
matin material  between  homologous  chromosomes  is  taken  into 
account.  The  condition  of  independent  distribution  although  simple 
in  itself  results  in  a  rapid  increase  in  complexity  with  the  increase  in  the 
number  of  pairs  of  chromosomes  involved. 

Chromosomes  and  sex  in  Drosophila. — The  relation  between 
inheritance  and  the  chromosome  mechanism  is  perhaps  most  simply 
displayed  in  the  inheritance  of  sex  in  those  animal  forms  in  which  the 
sexes  occur  in  approximately  equal  proportions.  Thus  in  Drosophila 
as  indicated  in  Fig.  75  there  are  three  pairs  of  autosomes  which  are 
alike  in  both  the  male  and  the  female.  The  remaining  pair  of  chromo- 
somes, however,  differ,  for  Ihe  female  possesses  two  X-chromosomes 
whereas  in  the  male  a  single  X-chromosome  is  paired  with  a  Y-chromo- 
some  and  these  differences  are  characteristic  of  all  normal  males  and 
females  of  this  species.  The  bearing  of  these  differences  on  the 
inheritance  of  sex  is  shown  diagrammatically  in  Fig.  75.  Beginning 
with  the  parents,  the  diploid  number  is  shown  in  the  circles  represent- 
ing the  female  and  the  male. 

In  the  female  the  three  pairs  of  autosomes  are  outlined  and  the 
X-chromosomes  only  are  drawn  in  black  to  indicate  that  they  are 
the  ones  primarily  concerned  in  the  determination  of  sex.     Similarly  in 


THE  PHYSICAL  BASTS  OF  MENDELISM 


411 


the  male  the  three  pairs  of  autosomes  which  are  exactly  like  those  in  the 
female  are  outlined,  but  the  X-chromosome  and  the  Y-chromosome  are 
drawn  in  black.     The  reduction  division  in  the  female  results  in  a 


Fig.  75. — Diagram  to  show  chromosome  relations  in  the  inheritance  of  sex 
in  Drosophila  ampelophila.     {From  Bahcock  and  Clausen.) 


separation  of  the  members  of  each  pair  of  chromosomes,  so  that  every 
secondary  germ  cell  (or  egg)  contains  two  large  curved  autosomes, 
a  small  autosome,  and  an  X-chromosome.  Consequently  as  far  as 
chromosome  content  goes  the  eggs  are  all  exactly  alike.     In  the  male, 


412     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

however,  the  separation  of  the  members  of  the  chromosome  pairs 
results  in  sperms  half  of  which  contain  an  X-chromosome  and  half  a 
Y-chromosome  in  addition  to  the  three  autosomes.  The  reduction 
division  in  the  male  insures  an  equality  in  numbers  for  the  two  kinds 
of  sperm  cells  and  the  chances  that  either  kind  of  sperm  will  fertilize 
an  egg-cell  are  equal.  By  this  arrangement  the  numerical  equality 
of  the  sexes  is  maintained.  When,  later,  the  egg  cells  of  the  female  are 
fertilized  by  the  sperm  cells  of  the  male,  as  shown  in  the  lower  portion 
of  the  figure,  half  of  them  being  fertilized  by  sperm  cells  which  contain 
an  X-chromosome  will  give  females,  and  half  uniting  with  sperm  cells 
which  contain  Y-chromosomes  will  produce  males.  The  inheritance 
of  sex  in  Drosophila  provides  a  beautiful  illustration  of  the  parallel 
behavior  of  the  chromosome  mechanism  and  a  somatic  difference,  in 
this  case,  sex. 

To  recapitulate,  the  essential  phenomena  of  cell  behavior  which  fur- 
nish the  mechanism  for  the  distribution  of  hereditary  factors  are  these : 

1 .  Every  species  is  characterized  by  a  definitely  organized  group 
of  chromosomes.  The  chromosomes  occur  in  pairs,  in  each  of  which 
one  member  is  derived  from  each  parent.  In  ordinary  somatic  mitosis 
the  distribution  of  chromatin  is  such  that  each  daughter  cell  receives 
a  full  complement  of  chromosomes  which  are  equivalent  qualitatively 
to  those  of  the  mother  cell. 

2.  In  germ  cell  formation  the  homologous  chromosomes  conjugate 
during  synapsis,  then  separate,  and  pass  into  a  division  figure  in  which 
entire  homologous  chromosomes  are  opposed  to  each  other.  The 
resulting  reduction  division  gives  daughter  cells  with  half  the  number 
of  chromosomes  characteristic  of  the  species,  the  half  number  being 
made  up  of  one  member  of  each  pair  of  chromosomes.  During  synap- 
sis there  is  an  opportunity  for  the  members  of  a  pair  of  chromosomes 
to  exchange  chromatin  material.  When  such  interchange  takes  place 
equivalent  portions  of  chromosomes  both  qualitatively  and  quantita- 
tively are  involved.  In  the  reduction  division  segregation  within  one 
pair  of  chromosomes  is  entirely  independent  of  that  of  any  other  pair 
so  that  the  combinations  of  parental  chromosomes  in  the  germ  cells 
represent  all  those  to  be  expected  on  the  basis  of  chance  distribution. 

The  student  should  constantly  endeavor  to  harmonize  this  con- 
ception of  the  distributing  mechanism  of  the  chromatin  material  with 
the  Mendelian  interpretations  of  hereditary  phemomena  which  will  be 
presented  in  what  follows,  to  the  end  that  he  may  obtain  a  clear  and 
definite  idea  of  the  interrelations  between  the  known  facts  of  heredity 
and  cell  behavior. 


CHAPTER  XXIX 
NEO-MENDELISM  IN  PLANTS^ 

JOHN   M.    COULTER    AND   MERLE    C.    COULTER 

Thus  far  we  have  been  considering  Mendel's  law  in  its  simple  form 
and  have  enlarged  but  little  upon  Mendel's  original  statement.  The 
value  of  the  law  is  apparent.  Upon  its  republication  in  1900  it  was 
taken  up  by  biologists  and  numerous  breeders  set  to  work  to  test  it. 
As  a  consequence  data  for  and  against  it  began  to  accumulate.  As 
might  be  expected,  there  was  much  apparent  evidence  against  the  law, 
but  as  geneticists  developed  a  better  conception  of  the  mechanism  the 
contradictory  evidence  was  explained  away.  Almost  every  type  of 
inheritance  has  now  been  explained  according  to  Mendel's  law.  Some 
of  the  explanations  are  very  complicated  and  cannot  be  included  in 
this  presentation.  A  few  of  the  more  important  cases,  however,  will 
be  presented. 

I.      PRESENCE    AND   ABSENCE   HYPOTHESIS 

This  may  be  regarded  as  a  new  method  of  Mendelian  thought.  It 
was  first  suggested  by  Correns,  but  later  was  worked  out  in  detail  by 
other  geneticists,  especially  Hurst,  Bateson,  Shull,  and  East.  It  is 
merely  a  modification  of  the  mechanism  involved.  For  example,  in 
the  case  of  a  hybrid  obtained  by  crossing  tall  and  dwarf  parents  the 
result  had  been  explained  as  due  to  the  fact  that  one  chromosome  bears 
a  determiner  for  tallness  and  the  other  one  of  the  pair  carries  the  deter- 
miner for  dwarfness.  In  other  words,  each  one  of  a  pair  of  allelo- 
morphs is  represented  by  a  determiner,  two  determiners  thus  being 
present.  Dwarfness  in  this  case  would  be  the  result  of  the  interaction 
of  that  determiner  and  its  environment  during  the  development  of  the 
body;  and  the  same  for  tallness.  When  both  were  present ,  however, 
the  conception  of  the  situation  was  as  follows.  The  determiner  for 
dwarfness,  setting  up  its  usual  series  of  reactions,  early  became  para- 
lyzed by  the  determiner  for  tallness  or  its  products.  This  result  was 
called  the  dominance  of  the  character  for  tallness.  It  was  as  if  the 
determiner  for  tallness  completely  prevented  the  activity  of  the  deter- 
miner for   dwarfness.      This  conception  was  apparently  borne  out 

»  From  Coulter  and  Coulter,  Plant  Genetics  (The  University  of  Chicago  Press, 
copyright  191 8). 

413 


414     READINGS  IN  EVOLUTION,    GENETICS,  AND  EUGENICS 

by  the  facts  and  was  the  explanation  of  the  mechanism  generally 
accepted. 

According  to  the  presence  and  absence  hypothesis,  however,  the 
situation  is  looked  at  from  an  entirely  different  point  of  view.  Tall- 
ness  is  the  result  of  a  determiner,  but  dwarfness  is  merely  the  result 
of  the  absence  of  the  determiner  for  tallness.  The  dominant  character 
is  produced  by  an  inheritable  determiner,  but  the  recessive  character 
appears  only  when  the  dominant  determiner  is  lacking.  This  con- 
ception has  some  evident  advantages  and  may  modify  the  previous 
Mendehan  diagram,  as  shown  in  Fig.  76.  This  appears  to  be  a  simpler 
mechanism  to  account  for  the  phenomenon  c'alled  dominance.  In  the 
case  of  the  dwarf  form  there  is  a  normal  course  of  development;  in  the 
case  of  the  tall  parent  or  hybrid,  however,  an  additional  determiner 


Dwarf  Parent 


Gametes 


Fig.  76. — Diagram  showing  how  the  original  scheme  must  be  modified  to 
satisfy  the  presence  and  absence  hypothesis.     {From  Coulter  afid  Coulter.) 


stimulates  cell  growth,  or  cell  division,  or  both.  It  is  a  simpler  and 
more  useful  conception,  so  long  as  it  fits  the  facts.  Some  investigators, 
however,  claim  that  it  cannot  be  applied  to  all  the  situations  that  have 
been  discovered. 

This  hypothesis  introduces  some  additional  terminology  suggested 
by  Bateson.  In  our  illustration  the  tall  parent  has  two  determiners 
for  tallness  and  therefore  Bateson  calls  it  duplex,  having  a  double  dose. 
For  the  same  reason  the  Fi  individuals,  having  only  one  determiner  for 
tallness,  he  calls  simplex.  According  to  the  same  terminology  the 
dwarf  parent  is  nulliplex  with  respect  to  its  character  of  tallness. 

Additional  advantages  of  the  presence  and  absence  hypothesis  will 
appear  in  connection  with  a  consideration  of  blending  inheritance  and 
of  cumulative  factors  in  inheritance.  Attention,  however,  should  be 
called  to  the  fact  that  those  who  accept  the  presence  and  absence 


neo-:mendelism  in  plants 


415 


hypothesis  do  not  use  the  form  of  notation  thus  far  used  in  explaining 
Mendehan  inheritance.  Assume  that  T  is  used  to  express  the  deter- 
miner for  tallness,  its  same  letter  (/)  is  used  to  express  the  absence. 
For  example,  instead  of  using  D  for  dwarfness,  /  is  used  for  '*  lack  of 
tallness"  (Fig.  77).  It  is  a  matter  of  convenience  to  have  a  symbol 
to  represent  the  recessive,  the  absence  of  something  that  is  present  in 
another  individual. 

In  summary,  the  essential  difference  between  the  presence  and 
absence  hypothesis  and  that  of  dominant  and  recessive  is  that  in 
the  former  case  the  recessive  determiner  has  no  existence  at  all, 
while  in  the  latter  case  it  exists,  but  is  in  a  latent  condition  when 
associated  with  the  dominant. 


Dwarf  Parent 


Gameti 


es 


Fig.  77. — Diagram  showing  how  presence  and  absence  scheme  is  actually 
used,  with  small  letter  representing  ''absence."     {From  Coulter  and  Coulter.) 


II.      BLENDS 

This  type  of  inheritance  when  first  discovered  was  thought  to  be 
in  direct  conflict  with  Mendel's  law.  It  is  a  case  in  which  dominance 
seems  to  fail,  for  the  two  alternative  characters  both  express  them- 
selves and  the  result  is  an  average  between  them.  It  is  easy  to  explain 
this  situation  in  accordance  with  the  presence  and  absence  hypothesis 
without  any  violation  of  Mendel's  law. 

The  classic  example  of  blending  inheritance  was  presented  by 
Correns  in  breeding  work  upon  Mirabilis  Jala  pa,  the  common  four- 
o'clock.  Correns  crossed  red  and  white  varieties,  and  all  the  hybrid 
progeny  had  rose  pink  flowers.  This  was  a  color  blend,  distinctly 
intermediate  between  the  colors  of  the  two  parents.  The  Fi  genera- 
tion, therefore,  seemed  to  contradict  Mendel's  law  in  that  one  color 
character  was  not  completely  dominant  over  the  other.  The  real  situa- 
tion, however,  appeared  in  the  F2  generation  obtained  by  inbreeding 


4i6     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

individuals  of  the  Fi  generation  which  showed  the  blend.  By 
inbreeding  the  pink  hybrids  Correns  obtained  the  perfect  1:2:1  ratio, 
that  is,  I  red  like  one  grandparent,  2  pink  like  the  hybrid  parent,  and 
I  white  like  the  other  grandparent.  Segregation  was  evidently  taking 
place,  the  only  unusual  thing  being  the  appearance  of  the  Fi  indi- 
viduals, and  that  was  explained  immediately  as  failure  of  dominance 
(see  Fig.  78). 

The  question  this  introduces,  therefore,  is  that  of  a  mechanism 
which  could  account  for  such  a  result.  The  easiest  explanation 
offered  is  that  the  red  parent  was  a  homozygote  for  redness  (double 
dose)  and  the  hybrid  a  heterozygote  (single  dose) ;  the  inference  is  that 


®    ® 


Red  Parent 


Gamete 


White  Parent 


(R)pinkQ 


Eggs 


Sperms 


®..® 


0P.® 


®P.0 


0   0 


Fig.  78. — Diagram  illustrating  blending  inheritance,  discovered  by  Correns 
in  Mirabilis  Jalapa.     {From  Coulter  and  Coulter.) 


a  single  dose  produces  pink  while  a  double  dose  produces  red.  A 
theoretical  explanation  of  this  occasional  difference  in  the  result  of 
double  and  single  doses  is  as  follows.  Imagine  that  the  body  cells 
of  a  plant  have  a  certain  capacity  for  expressing  hereditary  characters. 
In  such  a  case,  just  as  a  given  quantity  of  solvent  can  dissolve  only  a 
given  amount  of  solute,  so  the  body  cells  can  express  hereditary  charac- 
ters only  to  a  definite  limited  extent.  In  the  four-o'clock  a  single  dose 
of  redness  may  be  thought  of  as  half  saturating  the  body  cells,  while  a 
double  dose  completely  saturates  them.  In  cases  showing  complete 
dominance,  however,  a  single  dose  completely  saturates  the  cells  and  a 
double  dose  can  do  nothing  more.  This  analogy  assists  in  visualizing 
on  the  one  hand  the  necessary  mechanism  of  blends  (apparent  failure 


NEO-MENDELISM  IN  PLANTS  417 

of  dominance)  and  on  the  other  hand  that  for  cases  of  complete  domi- 
nance. 

Another  example  of  simple  blending  inheritance  is  the  case  of 
Adzuki  beans,  described  by  Blakeslee.  In  this  bean  the  mottling  of 
the  seed  coat  is  dominant  to  the  lack  of  mottling.  In  the  hybrid 
condition,  however,  the  mottling  is  lighter  than  in  the  pure  or  homo- 
zygous condition.  Heterozygous  plants,  therefore,  can  be  easily  dis- 
tinguished from  homozygous  plants,  so  that  the  1:2:1  ratio  is  evident 
on  externa]  inspection  rather  than  the  usual  3 :  i  ratio. 

III.      THE   FACTOR   HYPOTHESIS 

Mendel  concluded  that  each  plant  character  depends  upon  a  single 
determiner.  Inheritance,  however,  has  proved  to  be  a  much  more 
complex  phenomenon  than  indicated  by  Mendel's  peas.  Ratios  have 
appeared  that  were  puzzling,  and  geneticists  were  forced  to  the  conclu- 
sion that  there  may  be  a  compound  determiner  for  a  single  character. 
This  conception  is  called  the  factor  hypothesis,  and  the  growing  com- 
plexity of  genetics  has  developed  in  connection  with  this  hypothesis. 
With  the  consideration  of  factors  instead  of  determiners  one  passes 
from  elementary  to  advanced  genetics.  Previously  we  have  used  the 
word  determiner,  implying  Mendel's  idea  that  a  single  determiner  is 
responsible  for  the  development  of  a  plant  character,  and  this 
has  been  true  of  the  examples  of  inheritance  previously  considered. 
It  is  understood  now,  however,  that  a  character  is  frequently  deter- 
mined by  the  interaction  of  two  or  more  separately  heritable  factors, 
and  hence  the  factor  hypothesis.  The  distinction  between  factors  and 
determiners  should  be  made  clear.  In  case  only  one  factor  is  involved 
in  determining  a  character,  there  is  no  distinction  between  factor  and 
determiner;   and  in  such  a  case  the  term  factor  should  not  be  used. 

I.  Complementary  factors. — This  is  the  simplest  expression  of 
the  factor  hypothesis  and  it  may  be  illustrated  by  some  of  East's  work. 
Crossing  red-grained  and  white-grained  corn  he  obtained  all  red  in 
the  F2  generation.  This  would  suggest  that  the  F2  generation  would 
show  3  red  to  i  white;  but  it  showed  9  reds  to  7  whites,  which  did  not 
suggest  Mendelian  inheritance.  It  is  in  accord  with  Mendel's  law, 
however,  if  we  consider  that  two  complementary  factors  are  necessary 
to  produce  the  red  character,  and  that  each  of  these  factors  is  inherited 
separately.  Such  a  situation  would  give  a  dihybrid  ratio,  as  indicated 
in  Fig.  79.  It  will  be  seen  that  out  of  16  progeny  9  will  be  red,  for  they 
alone  contain  the  complementary  factors;  the  other  7  will  be  white. 


4i8     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

The  situation  is  thus  explained  by  the  dihybrid  ratio,  but  although 
only  one  character  is  involved  that  character  depends  upon  two  com- 
plementary factors. 

Another  situation  is  worth  noting.     No.  6  of  the  diagram  is  white 
because  it  contains  only  one  of  the  necessary  factors;  No.  ii  is  white 


Fig.  79. — Diagram  illustrating  behavior  of  complementary  factors  in  cross 
between  red-grained  and  white-grained  corn.  R  and  C  must  both  be  present  to 
produce  red-grained  corn.     {From  Coulter  and  Coulter.) 


for  the  same  reason,  but  its  germinal  constitution  is  just  the  opposite. 
What  would  happen  if  these  two  are  crossed?  There  is  only  one 
possibility,  since  each  is  a  homozygote  producing  only  one  kind  of 
gamete.  The  result  would  be  red,  and  thus  a  cross  between  two  whites 
would  produce  only  reds.  What  would  happen  from  crossing  Nos.  6 
and  15,  the  former  being  a  homozygote  and  the  latter  a  heterozygote  ? 


NEO-MENDELISM  IX  PLANTS  419 

It  is  obvious  that  the  resulting  progeny  would  be  one-half  white  and 
one-half  red,  although  both  parents  are  white.  The  same  result  would 
be  secured  in  crossing  Nos.  11  and  14.  A  cross  between  Nos.  14  and 
15,  both  of  which  are  heterozygotes,  would  result  in  3  whites  and  i  red, 
the  ordinary  3:1  ratio.  These  illustrations  show  how  diilerently  the 
same  phenotype  may  behave  in  inheritance.  In  each  case  two  whites 
were  crossed,  that  is,  the  same  phenotypes,  but  three  different  ratios 
were  obtained  because  the  genotypes  were  different. 

The  striking  feature  of  this  situation  is  that  one  can  cross  two 
whites  and  get  a  red.  This  gives  an  insight  into  the  so-called  phenome- 
non of  reversion.  For  example,  in  the  course  of  numerous  breeding 
experiments  Bateson  obtained  two  strains  of  white  sweet  peas,  each 
of  which  when  normally  "selfed''  bred  true  to  the  white  color;  but 
when  these  two  were  artificially  crossed  all  the  progeny  had  purple 
flowers,  like  the  wild  Sicilian  ancestors  of  all  cultivated  varieties  of 
the  sweet  pea.  This  appeared  to  be  a  typical  case  of  reversion.  Fur- 
ther breeding,  however,  showed  that  this  was  just  such  a  case  of  com- 
plementary factors  as  we  have  been  considering.  One  of  Bateson's 
white  strains  had  one  of  the  factors  for  purple  and  the  other  strain  had 
the  other  factor. 

Complementary  factors  have  been  defined  and  the  method  of  their 
Inheritance  described,  but  is  there  any  mechanism  to  explain  the 
situation?  A  suggestion  may  be  obtained  from  plant  chemistry. 
The  most  prominent  group  of  pigments  in  plants  is  the  group  of  antho- 
cyanins,  which  are  produced  as  follows.  Plants  contain  compounds 
called  chromogens,  which  are  colorless  themselves  but  which  produce 
pigments  when  acted  upon  by  certain  oxidizing  enzymes  or  oxidases. 
This  is  a  sufficient  mechanism  for  the  behavior  of  complementary 
factors.  If  one  of  East's  white  strains  of  corn  contained  a  chromogen 
capable  of  producing  red  but  lacked  the  necessary  oxidase  it  would 
remain  colorless.  If  the  other  white  strain  contained  the  oxidase  but 
no  chromogen  it  would  remain  colorless.  In  crossing  them,  however, 
chromogen  and  oxidase  would  be  brought  together  and  a  red-grained 
hybrid  would  be  the  result.  Inbreeding  such  red-grained  individuals 
of  course  would  give  red  and  white  progeny  in  a  ratio  of  9:7,  as 
explainedin  connection  with  East's  corn.  This  seems  to  be  the  explana- 
tion of  the  behavior  of  complementary  factors  in  many  cases  of  color 
inheritance. 

Where  other  characters  are  involved  the  mechanism  must  be  some- 
what  difTerent.     In  some  cases  the  two  factors  mav  be  the  enzvme 


420     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

and  the  compound  the  enzyme  attacks,  as  in  the  oxidase  and  chromo- 
gen  situation  just  described.  On  the  other  hand,  we  might  be  deahng 
with  two  chemical  compounds  that  are  inert  when  occurring  separately 
but  active  when  brought  together,  active  in  such  a  way  as  to  produce 
a  distinctly  new  character.  Also  two  active  substances  might  neutral- 
ize one  another  when  brought  together  in  a  hybrid,  and  the  failure  in 
their  activity  might  result  either  in  a  new  character  or  the  failure  of 
some  parental  character  to  develop.  Such  are  some  of  the  possible 
mechanisms  to  explain  the  behavior  of  complementary  factors. 

Hybridizing,  therefore,  is  much  like  mixing  chemicals  in  a  test 
tube.  We  know  that  very  wide  crosses  cannot  be  made  successfully; 
but  the  surprising  thing  is  that  certain  very  close  crosses  are  constantly 
unsuccessful,  even  though  both  parents  may  cross  freely  with  closely 
related  types.  We  obtain  a  glimpse  of  the  possibility  of  such  appar- 
ently inconsistent  behavior  when  we  consider  the  chemical  possibilities 
suggested  by  the  behavior  of  complementary  factors. 

The  origin  of  complementary  factors  is  an  interesting  field  of 
speculation.  Did  they  originate  together  or  separately?  A  natural 
inference  would  be  that  they  originated  together,  for  neither  would  be 
of  any  use  without  the  other.  It  should  be  remembered,  however, 
that  the  idea  of  use  as  explaining  the  occurrence  of  everything  in  a 
plant  is  being  abandoned;  one  must  think  rather  of  a  plant  as  a  com- 
plex physico-chemical  laboratory.  No  one  claims  that  all  chemical 
reactions  are  useful;  they  are  simply  inevitable ;  and  plant  characters 
are  the  result  of  chemical  reactions  and  physical  necessities.  Even 
though  we  assume  the  simultaneous  origin  of  two  complementary 
factors,  they  would  have  to  be  put  on  separate  chromosomes,  for  the 
factors  are  separately  inherited. 

The  other  alternative  is  to  suppose  that  these  factors  originated 
independently  in  the  history  of  a  plant.  In  this  case,  of  course,  the 
first  one  to  be  produced  would  remain  functionless  until  finally  its 
complement  came  into  existence.  This  might  be  an  explanation  of  what 
are  called  latent  characters.  Also  they  might  have  not  only  originated 
independently  but  in  different  varieties  or  species.  In  this  case  if 
natural  hybridizing  should  bring  them  together  the  result  would  be 
the  appearance  of  a  new  character,  and  this  may  have  been  a  very 
important  factor  in  the  origin  of  species. 

This  may  serve  as  an  introduction  to  the  factor  hypothesis,  with 
complementary  factors  as  an  illustration,  simply  because  it  is  the 
simplest  situation.     There  are  many  other  kinds  of  factors  recognized, 


NEO-MENDELISM  IN  PLANTS 


421 


but  we  shall  not  attempt  to  list  all  of  the  proposed  t\pes.     A  simple 
illustration  of  the  better  known  types  is  as  follows: 

a)  A  complementary  factor  is  added  to  a  dissimilar  factor  to  pro- 
duce a  particular  character. 

b)  An  inhibitory  factor  prevents  the  action  of  some  other  factor. 

c)  A  supplementary  factor  is  added  to  a  dissimilar  factor  with  the 
result  that  the  character  is  modified  in  some  way. 

d)  A  cumulative  factor,  when  added  to  another  similar  factor, 
affects  the  degree  of  development  of  the  character. 

Some  examples  of  these  types  will  make  them  clear,  those  for 
complementary  factors  having  been  given  previously. 


Pure  Red  Parent 


Gamete 


Gamete 


White  Parent  with 
Red  Inhibitor 


Fig.  80. — Diagram  illustrating  behavior  of  inhibitory  factor. 
and  Coulter.) 


{From  Coulter 


2.  Inhibitory  factors. — Recalling  East's  experiment  with  red- 
grained  corn  it  will  be  remembered  that  when  both  factors  for  red 
were  present  the  grain  was  red,  but  when  either  factor  was  absent  the 
grain  was  white.  Later  he  crossed  these  strains  with  a  new  white 
strain,  and  the  result  was  surprising.  The  pure  red  strain  produced 
gametes  carrying  both  the  red  factors,  and  it  would  be  expected  that 
whatever  such  a  gamete  mated  with  would  result  in  red  progeny;  but 
when  this  pure  red  was  crossed  with  the  new  strain  of  white  the  pro- 
geny were  all  white,  although  the  hybrids  certainly  contained  both 
factors  for  red.  The  explanation  which  first  occurred  to  East,  and 
which  later  experiments  confirmed,  was  that  the  new  white  strain  con- 
tained an  inhibitory  factor,  which  prevented  the  development  of  red 
even  though  both  the  complementary  factors  for  red  were  present. 


422     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 


Fig.  80  illustrates  the  situation  and  shows  why  all  the  individuals  of 
the  Fi  generation  are  white.  It  is  interesting  to  note  further  the 
possibilities  of  white  and  red  in  the  F2  generation.    They  would  be 


^ — ^ 


Red 


R^ 


White 


White 
Fig.  81. — Diagram  showing  some  possible  combinations  in  F2  when  Fi  of 
Figure  80  is  inbred.  Individual  on  left  end  of  upper  set  red-grained,  because  R 
and  C  both  present  and  /  absent;  other  individuals  in  upper  set  white,  because 
lacking  C  or  i?  or  both;  individuals  in  lower  set  with  inhibitory  factor  and  there- 
fore white,  whatever  other  combinations  of  factors  they  may  contain.  {From 
Coulter  and  Coulter.) 


numerous,  since  we  are  dealing  with  trihybrid  ratios  (see  Fig.  81). 
This  does  not  exhaust  the  possibilities,  for  the   cases  given  were 

honiozygotes,  each  producing  a  single  kind  of 
gamete.  There  remains  for  consideration  the 
heterozygote  situation  (see  Fig.  82). 

The  possible  mechanism  of  the  inhibitory 
factor  is  as  follows.  We  have  assumed  that  red  is 
produced  only  when  the  enzyme  is  present  to 
oxidize  the  chromogen.  Enzymes  are  very  sensi- 
tive; their  activities  may  be  affected  or  com- 
pletely checked  by  various  agents.  Suppose  that 
I  of  the  diagram  be  such  an  agent  and  the  neces- 
sary mechanism  is  apparent.  When  /  is  present  R  is  paralyzed,  so 
that  it  cannot  oxidize  C. 

3.  Supplementary  factors. — A  supplementary  factor  is  one  that  is 
added  to  a  dissimilar  factor,  with  the  result  that  a  character  is  modified 
in  some  way. 


0 

0 

© 

0 

0 

© 

Fig.  82. 

—  (From 

Coulter  and  Coulter.) 

NEO-MENDELISM  IX  PLANTS 


423 


In  his  work  upon  red-grained  races  of  corn  East  found  occasionally 
a  few  purple  grains.  His  conception  of  the  situation  is  as  follows. 
The  pure  red  plant  contains  two  complementary  factors,  one  (C)  a 
chromogen,  and  the  other  (R)  an  enzyme,  which  when  brought 
together  produced  the  red  color.  The  purple  grains,  however,  must 
be  explained  by  the  presence  of  still  another  factor  (P),  the  resulting 
situation  being  represented  in  Fig.  S^.  Of  course  when  C  is  absent 
no  pigment  whatsoever  can  be  produced.  As  a  consequence  we  will 
assume  that  the  presence  of  C  is  constant,  and  that  F  and  R  are  vari- 
ables. For  a  similar  reason  we  will  assume  that  the  absence  of  /  is 
constant.  The  figure  shows  three  possibilities,  from  which  the  follow- 
ing conclusions  may  be  drawn:  (i)  when  P  and  R  are  both  present 
the  result  is  purple  grains;  (2)  red  appears  only  in  the  absence  of  P; 
(3)  P  although  present  will  not  develop  any  color  in  the  absence  of  R. 


Purple 


® 

® 

® 

® 

© 

© 

© 

© 

Red 


White 


Fig.  83. — Diagram    illustrating    action    of    supplementary    factor. 
Coulter  and  Coulter.) 


(From 


This  is  a  typical  case  of  a  supplementary  factor,  that  is,  one  which 
is  added  to  a  dissimilar  factor,  with  the  result  that  the  color  character 
is  modified.  The  mechanism  of  this  situation  will  make  clearer  the 
behavior  of  the  supplementary  factor.  If  C  is  the  chromogen  and  R 
the  enzyme,  what  is  P?  The  suggested  answer  can  be  obtained 
from  plant  chemistry.  It  is  found  that  the  purple  pigment  is  produced 
by  the  same  substance  as  the  red,  but  represents  a  higher  state  of 
oxidation.  The  conclusion  is  obvious.  C  is  oxidized  by  7?  up  to  a 
certain  point,  where  red  is  produced;  but  if  P  is  also  present  it  repre- 
sents an  additional  enzyme,  which  attacks  the  red  pigment  and  oxidizes 
it  still  further  into  purple.  P  is  incapable  of  attacking  the  original 
chromogen,  but  when  R  carries  the  attack  to  a  certain  point,  P  can 
function  and  carry  the  oxidation  further.  As  a  consequence  P  without 
R  gives  white  grains,  while  R  gives  red  grains  only  in  the  absence  of  P. 


424     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

4.  Cumulative  factors. — These  will  be  considered  under  the  next 
heading,  ''Inheritance  of  quantitative  characters." 

In  addition  to  the  four  types  of  factors  given,  the  literature  of 
genetics  also  contains  discussions  on  intensifying  factors,  diluting 
factors,  distribution  factors,  etc.  These,  however,  do  not  introduce 
any  new  mechanisms. 

5.  Inheritance  of  quantitative  characters. — This  phase  of  the 
factor  hypothesis,  if  true,  is  of  fundamental  importance  not  only  to 
genetics  but  to  general  biology.  It  is  based  upon  the  conception  of 
cumulative  factors,  and  as  it  is  presented  it  will  be  realized  that  it 
throws  light  not  only  upon  numerous  breeding  experiments  but  also 
upon  variation  in  general,  which  means  evolution  also.  A  cumulative 
factor  was  defined  as  one  which,  when  added  to  another  similar  factor, 
affects  the  degree  of  development  of  the  character. 

It  will  be  recalled  that  Correns  crossed  red  and  white  strains  of 
Mirabilis  and  obtained  pink  hybrids.  The  suggested  explanation  of 
this  result  was  that  a  single  dose  of  the  red  determiner  gives  pink  while 
a  double  dose  gives  red.  When  Correns  inbred  these  pink  hybrids, 
he  obtained  the  result  presented  in  Fig.  78,  that  is,  i  red,  2  pink, 
I  white.     This  result  is  obvious  and  the  mechanism  is  plain. 

With  this  diagram  in  mind  we  shall  consider  some  of  the  experi- 
ments of  Nilsson-Ehle  at  the  Swedish  Experiment  Station.  He 
crossed  two  strains  of  wheat  with  red  and  white  kernels.  The  Fi 
individuals  had  light  red  kernels,  which  of  course  suggests  a  repetition 
of  the  situation  shown  by  Mirabilis  in  the  experiment  of  Correns. 
The  F2  generation,  however,  showed  a  very  different  result.  The  reds 
and  whites  appeared  in  the  ratio  of  15:1;  but  in  addition  to  this, 
among  the  15  reds  there  could  be  distinguished  varying  degrees  of 
redness.  Nilsson-Ehle  suspected  that  15:1  meant  a  dihybrid  ratio, 
16  individuals  being  necessary  to  give  the  ratio,  so  that  he  constructed 
the  tentative  scheme  shown  in  Fig.  84. 

This  shows  a  regular  dihybrid  ratio,  except  that  the  two  factors 
involved  are  similar.  Applying  the  single  dose  and  double  dose  con- 
ception, as  used  in  the  case  of  Corren's  pink  Mirabilis,  we  reach  the 
following  conclusions:  No.  i  only  has  four  doses  and  therefore  it  only 
is  deep  red;  Nos.  2, 3,  5,  9  have  three  doses  and  are  somewhat  lighter 
red;  Nos.  4,  6,  7,  10,  11,  13  have  two  doses  and  are  still  lighter  red; 
Nos.  8,  12,  14,  15  have  one  dose  and  are  very  light  red;  while  No.  16 
alone  has  no  dose  and  is  the  only  pure  white.  This  accounts  for 
the  15:1  ratio,  and  the  different  shades  of  red.     This  is  entirely  in 


NEO-MENDELISM  IN  PLANTS 


425 


accord  with  the  conceptions  that  have  been  presented,  and  only  two 
assumptions  are  necessary:  (i)  that  dominance  is  absent,  and  two 
doses  have  twice  the  effect  of  one:  (2)  that  the  independent  similar 
factors  are  cumulative  in  their  operation,  and  are  paired  with  their 
absence  in  the  hybrid.     This  was  Nilsson-Khle's  conception,  and  of 


Fig.  84. — Diagram  illustrating  Nilsson-Ehle's  explanation  of  15:1  ratio 
obtained  in  F2  generation  from  cross  between  red-grained  and  white-grained 
wheat.     {From  Coulter  atid  Coulter.) 

course  he  tested  it  by  further  experimental  work,  the  results  consist- 
ently confirming  the  conception. 

Since  it  is  important  to  fix  this  conception  clearly  in  mind,  another 
type  of  diagram  may  represent  the  facts  even  more  clearly.  The 
proportion  of  individuals  showing  the  various  degrees  of  redness  in  the 
F2  is  graphically  recorded  in  Fig.  85,  each  dot  representing  one  dose 
of  the  factors  in  question. 


426     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

Continuing  these  investigations,  Nilsson-Ehle  next  discovered  a 
new  strain  of  red-grained  wheat,  which,  when  crossed  with  the  pure 
white  strain,  yielded  Fj  hybrids  of  intermediate  intensity  of  red  as 
before.  The  F2  generation,  however,  showed  a  different  situation. 
Reds  and  whites  were  obtained  in  the  proportion  of  63 :  i ;  the  63  reds 
as  before  falhng  naturally  into  different  groups  on  the  basis  of  degree 
of  redness.     Applying  the  same  conception  as  before  Nilsson-Ehle 


#     # 


Pure  Red 


Grades  of  Pink 


White 


Fig.    85. — Another   method   of    visualizing  Nilsson-Ehle 's    15:1    ratio    (see 
Fig.  84).     {From  Coulter  and  Coulter.) 


discovered  that  in  this  case  he  was  dealing  with  a  trihybrid  situation. 
Without  constructing  the  usual  Mendel ian  diagram,  which  would  have 
to  be  extensive  enough  for  64  individuals,  the  situation  as  it  appeared 
in  the  F2  generation  may  be  represented  by  Fig.  86.  If  the  graph  is 
surmounted  by  a  curve  we  recognize  the  regular  ''probability  curve," 
exactly  the  kind  of  curve  biometricians  use  to  represent  the  fluctuating 
individuals  about  a  specific  type. 

This  conception  of  cumulative  factors,  therefore,  has  far-reaching 
significance.     For  a  long  time  biologists  have  recognized  individual 


NEO-MENDELISM  IX  PLANTS 


427 


variation  within  the  species.     Darwin  depended  upon  it  as  the  basis  of 
his  theory  of  natural  selection  as  the  origin  of  species;   in  fact,  ever 


Pure  Red 


liilt.'riiH'(li.iU'  Grades 


While 


Fig.  86. — Diagram   illustrating   Nilsson-Ehle's   63:1    ratio.     {From   Coulter 
and  Coidter.) 

since  Darwin's  Origin  of  Species,  individual  variation  has  been  funda- 
mental in  our  conceptions.  To  account  for  this  universally  recog- 
nized phenomenon,  Darwin  proposed  his  transportation  hypothesis  as 


428     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

a  possible  explanation,  which,  as  will  be  recalled,  did  not  long  sur- 
vive. Weismann  offered  in  explanation  his  germinal  selection,  which 
was  soon  discarded  because  it  was  beyond  the  possibility  of  experi- 
mental testing.  Aside  from  these  two  attempts  to  explain  individual 
variation  no  other  comprehensive  scheme  had  been  presented.  Biolo- 
gists had  simply  recognized  the  fact  of  individual  variation  without 
any  conception  of  the  mechanism.  They  knew  that  individual  varia- 
tion existed  but  had  even  stopped  asking  why  it  existed. 

The  importance  of  this  new  theory,  therefore,  is  obvious.  It  is 
an  ingenious  explanation  of  the  inheritance  of  quantitative  characters 
and  of  the  existence  of  individual  variations.  Furthermore,  the  theory 
has  not  been  developed  through  meditation,  but  has  its  basis  in 
scientific  experiments.  It  is  imaginative  to  a  certain  extent,  of  course, 
as  is  every  other  valuable  theory,  but  unlike  most  such  theories  it  has 
a  substantial  foundation,  namely,  Mendel's  law. 


CHAPTER  XXX 

NEO-MENDELIAN  HEREDITY  IN  ANIMALS 

H.  H.  Newman 

Immediately  after  the  announcement  by  De  Vries  in  1900  of  the 
rediscovery  of  Mendel's  paper,  zoologists  in  Europe  and  in  America 
began  experiments  in  animal  breeding  with  the  idea  of  discovering  to 
what  extent  Mendel's  laws  were  applicable.  It  was  soon  found  that 
the  principles  of  unit  characters,  dominance,  segregation,  mono- 
hybrid,  dihybrid,  and  trihybrid  ratios  were  of  practically  universal 
application.  A  number  of  instances  of  Mendelian  heredity  in  animals 
have  already  been  presented  in  the  preceding  chapter  and  no  more 
simple  Mendelian  cases  need  be  described.  For  a  considerable  period 
the  animal-breeders  proceeded  no  farther  in  their  analysis  of  the 
mechanism  of  heredity  than  Mendel  had  done  so  many  years  before. 
In  time,  however,  new  facts  came  to  light  that  needed  further  analysis, 
and  the  older  Mendelism  was  superseded  by  neo-Mendelism.  This 
new  phase  in  the  study  of  heredity  is  in  the  forefront  of  interest  today. 
Neo-Mendelian  heredity  in  plants  has  already  been  discussed.  It 
remains  for  us  to  present  the  data  on  some  phases  of  neo-Mendelism 
in  animals. 

ILLUSTRATIONS    OF   THE   FACTOR  HYPOTHESIS 
THE   FACTORIAL   ANALYSIS    OF    COLOR    IN    MICE 

Miss  Durham,  after  extensive  breeding  experiments  with  numer- 
ous strains  of  differently  colored  mice,  has  been  able  to  show  that 
the  appearance  of  a  particular  color  in  an  individual  mouse  is  depend- 
ent upon  the  presence  or  absence  of  several  independently  inherited 
factors,  evidently  represented  by  genes  in  as  many  different  chromo- 
somes.    It  seems  possible  to  classify  these  factors  as  follows: 

.5  =  black  pigment,  which  masks  chocolate  pigment 
b  =  absence  of  B,  which  gives  chocolate 

/  =  intensity  factor 

i  =  absence  of  intensity,  or  dilution  factor 

C  =a  complementary  color  factor  acting  with  F 
P=a  complementary  pigment  factor  acting  with  C 

If  either  C  or  P  are  absent,  albino  mice  result  no  matter  what 

other  color  factors  may  be  present. 

429 


430     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

The  factorial  make-up  of  the  various  mice  in  Miss  Durham's 
experiments  would,  then,  be  represented  as  follows: 

^/CP  =  black 

BiCP  =blue  (dilute  black) 

hICP  =  chocolate  (absence  of  black) 

hiCP   =  silver  fawn  (dilute  chocolate) 

The  following  experiments  indicate  the  mode  of  heredity  on  the 
factorial  basis: 

1.  P     Black  (^/CP)X Silver-fawn  {biCP) 
Fx        ICO  per  cent  Black  (BICP-biCP) 

Fj    Black   (BICP)   Blue   (BiCP)  Chocolate  (blCP)  Silver-fawn 

ibiCP) 
9331 

2.  P     Blue  (BiCP)XChoco\site  (blCP) 

Fi  100  per  cent  Black  (BiCP-blCP) 

F2    Black  {BICP)  Blue  (BiCP)   Chocolate  (bICP)   Silver-fawn 

(biCP) 
9  3  3  I 

3 .  P  Blue  (BiCP)  X  Silver-fawn  (biCP) 
Fx  100  per  cent  Blue  (BiCP-biCP) 
F,    Blue  (BiCP)  Silver-fawn  {biCP) 

3  I 

DIFFERENT   KINDS    OF    ALBINOS 

Any  one  of  the  color  types  mentioned,  if  lacking  in  the  factor  C, 
will  be  an  albino,  though  carrying  the  other  factors  for  color.  For 
example,  there  may  be  a  Black-albino  (BIcP),  a  Blue-albino  (BicP), 
a  Chocolate-albino  (bIcP),  or  a  Silver-fawn-albino  {bicP). 

That  color  factors  are  present  in  albinos  may  be  shown  by  the 
following  experiment.  An  albino  had  appeared  in  a  Black  stock  and 
was  crossed  with  a  Silver-fawn,  thus: 

4.  P     Silver-fawn   (^>^'CP)X Albino   extracted   from  Black   {BIcP) 
Fi        100  per  cent  Black  (biCP-BIcP) 

Black         Blue        Chocolate     Albino-Black     Silver-fawn 
(BICP)      (BiCP)         (bICP)  (BIcP)  (biCP) 

27  9  9  9  3 

Albino-Blue  Albino-Chocolate  Albino-Silver-fawn 

(BicP)  (bIcP)  (biCP) 


NEO-MEXDELIAN  HEREDITY  IX  AXIMALS 


431 


The  ratios  given  are  the  theoretical  ratios  for  a  trihybrid  Mendel- 
ian  experiment,  and  the  actual  results  have  closely  approximated  these. 
As  a  matter  of  fact,  sixteen  albinos  appeared,  and  it  is  not  possible, 
except  by  breeding,  to  tell  one  kind  from  another.  Breeding  each 
with,  for  example.  Silver-fawn  would  readily  reveal  the  differences; 
for  the  Fi  generation  would  all  be  of  the  color  that  is  masked  by  the 
lack  of  C  in  these  albinos.  In  the  language  of  Johanssen  there  is  only 
one  albino  phenotype,  but  there  are  four  albino  genotypes.  Similarly 
in  experiments  (i)  and  (4),  which  have  just  been  described,  the  indi- 
viduals are  all  Black  (phenotypically  identical),  but  that  they  are  not 
genotypically  alike  is  clearly  shown  by  inbreeding  them.  In  experi- 
ment (i)  we  get  only  individuals  of  the  four  color  types,  while  in 
experiment  (4)  we  get,  in  addition  to  the  four  color  types,  four  albino 
types. 

castle's  guinea  pigs 

Professor  W.  E.  Castle  was  one  of  the  first  zoologists  to  use  Men- 
del's methods.  He  soon  discovered  that  in  the  determination  of  the 
coat  characteristics  of  guinea  pigs  at  least  three  sets  of  factors  were 
necessary,  as  follows: 

C  =  colored  fur 

c  =  albinism   (absence  of  C) 

5  =  short  fur 

5  =  long  fur  (recessive  to  S) 

i?  =  rosetted  fur 
r  =  smooth  fur  (absence  of  R) 

An  example  will  show  how  these  factors  segregate: 
P      Colored,  Short,  Smooth  X  Albino,  Long,  Rosetted 

{CSr)  (csR) 

Fi        100  per  cent  Colored,  Short,  Rosetted  (CSr-csR) 


Colored 

Short 

Rosetted 
27 

Albino 

Long 

Rosetted 

3 


Colored 

Long 

Rosetted 

9 

Albino 
Long 

Smooth 

I 


Colored 

Short 

Smooth 

9 


Albino 

Short 

Rosetted 

9 


Colored 

Long 

Smooth 

3 


Albino 
Short 
Smooth 
3 


432      READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

The  ratio  of  27, 9,  g,  g,  3, 3,  3,  i  shows  clearly  that  the  three  factors 
independently  segregate  and  are  all  three  concerned  in  the  determi- 
nation of  the  characters  of  the  fur.  A  fourth  factor,  a  pattern  factor, 
is  often  present  that  further  complicates  the  factorial  analysis.  Usually 
the  self-color  dominates  the  pattern,  but  certain  special  patterns  are 
dominant  over  self-color. 

These  two  examples  for  animals  are  sufficient  to  illustrate  the 
nature  of  Mendelian  factors  and  their  workings.  Numerous  other 
factors  have  been  discovered.  Castle,  for  example,  found  a  factor 
associated  with  the  occurrence  of  brown  pigment  in  guinea  pigs. 
Some  rabbits  have  the  pigment  distributed  evenly  over  the  body; 
others  have  it  in  the  eye  only.  These  conditions  are  allelomorphic  to 
each  other,  E  (extension)  being  dominant  over  e  (restriction  to  eyes). 

Inhibiting  factors  are  distinguished,  the  presence  of  which  prevents 
the  appearance  of  a  character  represented  in  the  germ  plasm.  Lethal 
factors  result  in  the  loss  of  something  necessary  for  the  life  of  the 
individual.  Modifying  factors  change  the  expression  of  a  character 
that  depends  on  another  gene.  These  and  various  other  types  of 
factors  have  been  discovered  by  the  large  school  of  neo-Mendelians 
now  so  actively  at  work. 


CHAPTER  XXXI 

SEX-LINKED  AND  OTHER  KINDS  OF  LINKED  INHERIT- 
ANCE IN  DROSOPHILA  AND  OTHER  SPECIES^ 

WILLIAM    E.    CASTLE 

All  the  facts  of  sex-linked  inheritance  in  Drosophila  harmonize 
with  Morgan's  hypothesis  that  the  genes  of  sex-linked  characters  lie 
in  a  common  cell  structure  (X-chromosome)  which  is  duplex  in  females, 
simplex  in  males.  Accordingly,  in  a  race  which  breeds  true  for  a 
sex-linked  character,  that  character  may  be  transmitted  by  every  egg, 
but  by  only  half  the  sperms,  namely  by  such  as  possess  an  X-chromosome 
and  by  virtue  of  that  fact  determine  as  female  all  zygotes  into  which 
they  enter.  To  male  zygotes  the  sperm  will  not  transmit  sex-linked 
characters.  This  hypothesis  is  supported  by  some  curious  facts  already 
alluded  to  but  deserving  of  fuller  consideration  in  this  connection,  viz., 
facts  observed  in  reciprocal  crosses  involving  a  sex-linked  character, 
as  for  example  white-eye  in  Drosophila. 

TABLE  I 

Reciprocal  Crosses  of  White-eyed  with  Red-eyed  Drosophila 


Male               Female 

Male                             Female 

p 

White     X     Red 

Red           X         White 

Fx 

Red                Red 

White                      Red 

Fa 

I  Red:  i  White    Red 

I  Red:  i  White     i  Red:  i  White 

It  has  already  been  stated  that  a  white-eyed  male  Drosophila 
crossed  with  normal  females  has  only  normal  children  of  both  sexes, 
while  the  white-eyed  grandchildren  are  all  of  the  male  sex.  In  the 
reciprocal  cross,  between  a  white-eyed  female  and  a  normal  male  all 
the  daughters  are  normal,  but  the  sons  are  white-eyed,  and  among  the 
grandchildren  white-eyed  individuals  occur  in  both  sexes.  Diagrams 
will  best  explain  these  facts  on  the  basis  of  Morgan's  hypothesis. 
(See  Figs.  87  and  88  and  Table  I.) 

To  state  the  foregoing  facts  in  another  way,  it  will  be  observed  that 
the  recessive  sex-linked  character  in  Drosophila,  when  introduced  in  a 
cross  by  the  male  parent,  disappears  entirely  in  Fi  and  reappears  in  Yi 

^  From  W.  E.  Castle,  Genetics  and  Eugenics  (copyright  1920).  Used  by 
special  permission  of  the  publishers,  The  Harvard  University  Press. 

433 


434     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

only  in  male  individuals.  But  if  the  recessive  sex-linked  character  is 
introduced  by  the  female  parent,  it  appears  in  Fi  in  male  individuals 
but  in  F2  in  both  sexes. 

Suppose  now  a  cross  is  made  between  two  races,  each  of  which 
possesses  a  different  sex-linked  recessive  character,  as  for  example 
white  eye  and  yellow  body.    (See  Table  II,  p.  436.)    If  the  white-eyed 


Flies 


CliTOjnosomes 


6 


d 


9 

X      0      6 


Parents 


Gametes 


(^ 


XI  XX  X 

?  ?  C? 


Fi 


Gaifietes 


F2 


Fig.  87. — Sex-linked  inheritance  of  white  and  red  eyes  in  Drosophila.  Parents 
white-eyed  male  and  red-eyed  female;  Fi,  red-eyed  males  and  females;  Fj,  red- 
eyed  females  and  equal  numbers  of  red-eyed  and  white-eyed  males.  A  black 
X  indicates  an  X  chromosome  bearing  the  gene  for  red  eye,  a  white  X  bears  white 
eye.  (p)  indicates  that  X  is  wanting;  in  recent  publications  Morgan  replaces  it 
by  Y.     {From  Conklin,  after  Morgan.) 


parent  is  a  female,  there  will  be  produced  white-eyed  males  in  Fj 
and  white-eyed  flies  of  both  sexes  in  F2.  But  the  male  parent  being 
yellow,  there  will  be  no  yellow  flies  produced  in  Fj  and  only  yellow 
males  in  F2.  In  the  reciprocal  cross  (yellow  female  X  white-eyed 
male)  yellow  males  will  be  produced  in  Fi  and  yellow  flies  of  both  sexes 
in  F2,  while  white-eyed  flies  will  not  appear  until  F2  and  then  only  in 
the  male  sex.  In  either  of  the  reciprocal  crosses  we  expect  the  pro- 
duction in  F2  both  of  yellow-bodied  males  and  of  white-eyed  males. 


SEX-LINKED  INHERITANCE 


435 


Usually  no  other  sort  of  male  is  produced  throughout  the  experiment 
except  these  two,  but  occasionally  there  is  produced  a  male  both 
yellow-bodied  and  white-eyed,  or  one  which  is  gray-bodied  and  red- 
eyed,  like  wild  flies.  How  do  these  arise?  If  in  Fi  females  the 
paired  X's  were  to  exchange  loads  in  part,  so  that  G  and  R  came  to  be 
attached  to  the  same  X  and  g  and  r  to  the  other  X,  and  if  each  of  the 


Flies 


Chromosomes 


XX 

X     X     ? 


X  0 
iXi 
X      1 


XX  X^  X 

?     ?     d' 


Parents 


Gametes 


Fi 


Gametes 


Fz 


S 


Fig.  88. — Reciprocal  cross  to  that  shown  in  Figure  87.  Parents,  red-eyed 
male  and  white-eyed  female;  Fj,  white-eyed  males  and  red-eyed  females  ("criss- 
cross inheritance" — Morgan);  Fj  equal  numbers  of  red-eyed  and  white-eyed 
individuals  of  both  sexes.  The  distribution  of  the  sex  chromosomes  is  shown  at 
the  right,  as  in  Figure  87.     {From  Conklin,  after  Morgan.) 

eggs  having  such  a  constitution  were  to  be  fertilized  with  a  sperm 
which  lacked  X  (male  determining  sperm),  this  would  make  possible 
the  production  of  F2  males  possessing  both  dominant  characters  and 
others  possessing  both  recessive  characters  or  gray-red  and  yellow- 
white  respectively,  as  actually  observed  in  about  one  case  in  a  hundred 
by  Morgan. 

It  may  add  interest  to  the  case  to  state  parenthetically  that  in  man 
occur  a  number  of  sex-linked  variations  which  are  inherited  in  this  same 
curious  fashion.     Among  them  may  be  mentioned  color  blindness  and 


436     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

bleeding  {haemophilia),  which  occur  chiefly  in  males,  but  are  never 
transmitted  by  males  to  their  sons  but  only  through  their  daughters  to 
their  grandsons. 

Morgan  and  his  pupils  have  described  between  forty  and  fifty 
characters  in  Drosophila  which  are  sex-linked  in  heredity;   they  also 

have   discovered  a   large  number  of  other 
%X  Mendelizing  characters  in  Drosophila  which 

^•\\^  are  not  sex-linked  but  which  nevertheless  are 

inherited  in  groups,  characters  in  the  same 

Fig.  89.— Drawing      group  showing  coupling  when  introduced  in  a 
showing  the  four  pairs  .  010 

of  chromosomes  seen  in  cross  from  the  same  parent,  and  repulsion 
the  dividing  egg  of  Droso-  when  introduced  from  different  parents.  The 
phila.    (After  Dr.  C.E.V.      number  of  these  groups  exactly  corresponds 

with  the  number  of  the  chromosomes  and 
Morgan  believes  that  their  genes  are  located  in  the  chromosomes,  an 
hypothesis  which  seems  reasonable  but  which  would  be  severely  strained 
if  an  additional  group  of  characters  should  be  discovered.  There  are 
three  groups  of  the  non-sex-linked  characters.  (See  Fig.  90.)  In  one  of 
these  referred  to  as  Group  II  (the  sex-linked  group  being  called  Group 
I),  are  found  variations  known  as  black  body  and  vestigial  wings  respec- 
tively, together  with  some  thirty-five  other  variations.  In  Group  III 
are  found  the  variations  known  as  pink  eye,  spread  wings,  and  ebony 
body,  together  with  some  twenty  other  variations.  In  Group  IV  are 
included  as  yet  only  two  characters,  bent  wings  and  eyeless,  which  how- 
ever show  linkage  with  each  other.  No  inherited  characters  have  been 
discovered  in  Drosophila  which  are  not  inherited  in  one  or  another  of 
the  four  linkage  groups. 

TABLE  II 

Reciprocal  Crosses  of  White-eyed  and  Yellow-bodied  Flies 

Male  Female  Male  Female 

P      Yellow-red    X  Gray-white  Gray-white  X  Yellow-red 

Fi     Gray-white  Gray-red  Yellow-red  Gray-red 

J  I  Gray- white:  i  Gray-red:  i  Gray- white:  i  Gray- red: 

^  \  I  Yellow- red  i  Gray- white  i  Yellow-red  i  Yello\v-red 

DROSOPHILA   TYPE   AND   POULTRY   TYPE    OF    SEX-LINKED    INHERITANCE 

I.  Drosophila  type. — The  same  type  of  sex-linked  inheritance 
which  is  found  in  Drosophila  is  found  also  in  man,  in  cats  (inheritance 
of  yellow  color),  and  in  the  plants,  Lychnis  and  Bryonia.  The  essen- 
tial feature  of  the  "Drosophila  type"  of  inheritance  is  this.    In  a  race 


.0.0  YELLOW.  SPOT. 
-.Of  LKTflAL  I. 
«-0  A\  IIJTE.  EOSIN  CHERBV. 

a.o  AUNORMAL. 


•ao  STREAK. 


.0.0  SEPIA. 


••O  BIFID. 


•BEVT. 


14.'  CLfR 


■i».0  SHIFTED. 


■!•.•  DACeS. 


■  »•.»  LETHAL  irr. 

•a».a  TAN. 


'  a».o  riNK,  PEACH. 


•EYELESS. 


0) 

C 
o 


c 
o 


o 

c 
c 


'z:    -c 


C     r    -:2 


tA 


■33.0  VERMIUON. 
3«.a  Ml  MA  TUBE. 


•  -".T  LETH.4L  V. 
•■•9.0  SABLE. 


•»4.7  BLACK. 


-♦0.0  PURPLE. 


•■•o.  KIDNET. 


•■*•,»  LETHAL  IV. 


■MJ  RUDIMENTARY. 

»•••  FORKED. 
■»7.o  BARRED. 


•»».5  FUSED. 


•••.•  LETHAL  S. 


••a.0  VESTIGLAl. 


•e».EBONT.  SCOTT. 


•  •OA  CUBVED. 


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438     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

breeding  true  for  a  sex-linked  character,  the  female  is  homozygous 
for  the  character  in  question  while  the  male  is  heterozygous  and  incap- 
able of  becoming  homozygous.  Reciprocal  crosses  with  such  a  race 
give  unlike  results,  because  the  female  transmits  the  character  to  all 
her  offspring,  but  the  male_ transmits  it  to  only  half  his  offspring,  viz., 
the  females. 


Fig.  91. — Sex-linked  inheritance  of  barred  and  unbarred  (black)  plumage  in 
poultry.  P,  parents,  barred  male,  unbarred  female;  Fi,  barred  males  and  females; 
F2,  males  all  barred,  females  in  equal  numbers  barred  and  unbarred.  {After 
Morgan.) 


2.  Poultry  type. — Another  type  of  sex-linked  inheritance  exists  in 
which  the  sex  relations  are  exactly  reversed.  This  was  first  observed 
in  the  moth,  Abraxas,  but  more  familiar  cases  occur  in  poultry,  for 
which  reason  it  may  be  called  the  poultry  type  of  sex-lmked  inherit- 
ance. Here  the  male  is  the  homozygous  sex,  the  female  being  hetero- 
zygous.    This  condition  is  found  in  moths  and  in  certain  birds,  viz., 


SEX-LINKED  INHERITANCE 


439 


in  domestic  fowls,  pigeons,  ducks,  and  canaries.  As  an  example  we 
may  take  the  inheritance  of  the  color  pattern,  barring,  in  crosses  of 
barred  Plymouth  Rock  fowls.  In  reciprocal  crosses  between  pure- 
bred barred  Plymouth  Rocks  and  black  Langshans  (or  another 
unbarred  breed),  the  results  are  not  identical.  If  the  barred  parent  is 
the  male  (Fig.  91  and  Table  III),  all  Fi  ofTspring  are  barred  and  in  Fj 
all  males  are  barred,  but  half  the  females  are  black  and  half  are  barred. 
If,  however,  the  barred  parent  is  the  female  (Fig.  92  and  Table  III), 

TABLE  III 
Reciprocal  Crosses  of  Barred  and  Black  Breeds  of  Fowls 


Male                    Female 

Male                                  Female 

P      Barred      X      Black 

Black             X           Barred 

Fi     Barred              Barred 

Barred                        Black 

F2     Barred     i  Barred:  i  Black 

I  Barred:  i  Black     i  Barred:  i  Black 

(See  Fig.  91) 

(See  Fig.  92) 

Fig.  92. — Reciprocal  cross  to  that  shown  in  Fij^ure  91.  P,  parents,  unbarred 
male,  barred  female;  F,,  barred  males,  unbarred  females  (crisscross  inheritance); 
F2,  barred  and  unbarred  birds  equally  numerous  in  both  sexes.     {From  Ciisllc.) 


440     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

all  Fi  males  are  barred,  but  all  Fi  females  are  black.  In  F2  barred  birds 
and  black  birds  occur  in  both  sexes.  These  curious  facts,  which  have 
been  repeatedly  verified,  suggest  the  occurrence  of  a  vehicle  of  inherit- 
ance which  is  duplex  in  males  but  simplex  in  females.  What  this  is  we 
do  not  know.  No  chromosome  has  been  found  which  has  a  distribu- 
tion of  this  sort  in  fowls,  but  it  is  possible  that  some  chromosome 
component,  or  other  cell  constituent  has  such  a  distribution  and  may 
be  the  actual  vehicle  of  inheritance  in  such  cases.  The  most  important 
character  economically,  which  appears  to  be  affected  by  some  sex- 
linked  factor  in  poultry,  is  fecundity.  Pearl  has  shown  that  when 
reciprocal  crosses  are  made  between  Cornish  Indian  Games,  a  poor 
breed  for  winter  egg  production,  and  barred  Plymouth  Rocks,  a  fairly 


cm 


M 


O 


ur 


B 


M 


a 


Fig.  93-— -B  and  C  illustrate  Morgan's  idea  of  the  linear  arrangement  of  the 
genes  in  the  chromosomes.  A  and  D  show  how  the  composition  of  the  chromo- 
somes is  supposed  to  change  as  the  result  of  the  crossover.  On  the  right,  a  pair 
of  chromosomes,  a,  before;  h,  during;  and  c,  after  a  double  crossover.  {After 
Morgan.) 


good  breed  for  winter  egg  production,  the  Fi  females  in  each  case 
resemble  the  father's  race  more  strongly  than  the  mother's  race  as 
regards  egg  production.  Pearl  did  not  maintain,  however,  nor  do  his 
experiments  suggest,  that  the  inheritance  of  fecundity  depends  exclu- 
sively upon  a  sex-linked  factor.  Goodale,  however,  has  not  been 
able  to  confirm  Pearl's  observations,  in  the  case  of  Rhode  Island  Red 
fowls.  He  finds  no  evidence  of  superior  influence  of  the  sire  in  the 
transmission  of  racial  fecundity. 


CHAPTER  XXXII 
LINKAGE  AND  CROSSING-OVER^ 

WILLIAM   E.    CASTLE 

In  ordinary  Mendelian  inheritance,  if  two  characters,  A  and  B, 
enter  a  cross  in  the  same  gamete  (either  egg  or  sperm),  it  will  be 
wholly  a  matter  of  chance  whether  they  continue  together  or  are  found 
apart  in  the  following  generation.  If  in  the  formation  of  gametes  by 
the  cross-bred,  A  and  B  separate  from  each  other  and  pass  into  differ- 
ent gametes,  it  is  evident  that  one  of  them  has  crossed  over  from  the 
gametic  group  in  which  both  originally  lay  to  enter  the  alternative 
group.  This  event  may  be  called  simply  a  crossover.  Crossovers  and 
non-crossovers  will  be  equally  numerous  (50  per  cent  each)  where  no 
linkage  occurs.  Also,  if  A  and  B  enter  a  cross  in  different  gametes, 
one  in  the  egg,  the  other  in  the  sperm,  it  will  in  ordinary  Mendelian 
inheritance  be  a  matter  of  chance  whether  they  emerge  from  the 
cross  together  or  apart.  If  together,  it  is  evident  that  a  crossover 
has  occurred;  if  apart,  a  non-crossover,  that  is  a  persistence  of  their 
previous  relations.  Again,  crossovers  and  non-crossovers  will  be 
equally  numerous  (50  per  cent  each)  if  no  linkage  occurs. 

Linkage  may  be  defined  as  the  tendency  sometimes  shown  by  genes 
to  maintain  in  hereditary  transmission  their  previous  relations  to  each 
other.  Thus  if  two  linked  genes,  A  and  B,  enter  a  cross  together  in  the 
same  gamete,  they  will  oftener  than  not  be  found  together  in  the 
gametes  formed  by  fhe  cross-bred  individual.  Crossovers  in  that  case 
will  be  less  than  50  per  cent,  and  non-crossovers  more.  And  if  the 
same  two  genes  enter  the  cross  separately,  one  in  the  egg,  the  other  in 
the  sperm,  then  oftener  than  not  they  will  be  found  apart,  in  different 
gametes  formed  by  the  cross-bred  individual.  Again  crossovers  will 
be  less  than  50  per  cent. 

The  number  of  genes  in  a  linkage  group  varies  in  known  cases  from 
2  to  50  or  more.  However  many  genes  there  are  in  a  linkage  group, 
each  gene  shows  linkage  with  every  other  gene  belonging  to  the  same 
group,  but  the  apparent  strength  of  the  linkage  varies  greatly.  Under 
uniform  environmental  conditions,  A  and  B  show  a  fairly  constant 

^  From  W.  E.  Castle,  Genetics  and  Eugenics  (copyright  1920).  Used  by 
special  permission  of  the  publishers,  The  Harvard  University  Press. 

441 


442      READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

linkage  with  each  other,  A  and  C  show  a  different  and  likewise  fairly- 
constant  linkage  strength,  and  so  on  through  the  entire  group.  This 
leads  to  the  conclusion  that  the  genes  of  a  linkage  system  are  bound 
together,  gene  with  gene,  with  bonds  of  definite  strength  in  each  case. 
In  order  to  visualize  the  matter  and  get  a  more  objective  view  of  link- 
age relations,  Morgan  and  his  associates  have  developed  the  chromo- 
some theory  of  linkage.     Its  essential  parts  are: 

1.  Genes  which  show  linkage  with  each  other  are  located  in  the 
same  pair  of  chromosomes.  It  is  the  substance  of  the  chromosome 
which  binds  the  genes  to  each  other  and  causes  A  to  be  inherited 
when  B  is. 

2.  Genes  close  together  in  the  same  chromosome  show  strong  link- 
age, genes  farther  apart  show  less  linkage. 

3.  Homologous  chromosomes,  those  containing  corresponding  sets 
of  genes,  one  set  derived  from  the  father,  one  from  the  mother,  lie  side 
by  side  (in  synapsis)  previous  to  the  formation  of  gametes.  At  this 
time  breaks  are  likely  to  occur  in  the  chromosomes  and  parts  of  one 
are  likely  to  replace  corresponding  parts  of  the  other. 

4.  Such  replacement  is  called  crossing-over. 

5.  Breaks  are  commoner  in  long  chromosomes  than  in  short  ones, 
and  between  distant  points  than  between  near  points  on  the  same 
chromosome. 

6.  The  genes  occur  in  a  chromosome,  like  beads  on  a  string,  in  a 
single  row  and  in  definite  order. 

The  supposed  order  of  the  genes  in  the  four  linkage  groups  of  Dro- 
sophila  and  their  relative  distances  apart  are  shown  in  Fig.  90  (p.  437) . 
In  these  diagrams  or  "maps,"  when  the  probable  order  of  the  genes 
in  a  system  has  once  been  determined,  the  supposed  end  gene  of  the 
system  is  placed  at  position  o  and  the  gene  next  to  it  is  placed  at  a 
distance  (in  centimeters  or  other  units)  corresponding  to  the  average 
cross-over  percentage  between  the  two,  this  process  being  repeated 
from  gene  to  gene  until  the  whole  chain  is  plotted.  The  "map"  is 
thus  based  on  a  summation  of  the  distances  (measured  in  cross-over  per- 
centages) from  gene  to  gene.  But  if  we  compare  the  "map  distances" 
between  genes  not  adjacent  to  each  other  in  the  chain  with  the  observed 
cross-over  percentages  between  the  same  genes,  we  find  that  the  map 
distance  is  regularly  greater  than  the  cross-over  percentage,  except  for 
very  short  distances  (5  or  less).  Thus  if  three  genes  occur  in  the  order 
ABC,  it  is  usually  found  that  AB+BC  is  greater  than  AC.  In  other 
words,   the  cross-over  percentage  between   B  and  C   is  commonly 


LINKAGE  AND  CROSSL\G-OVER  443 

greater  than  the  cross-over  percentage  between  A  and  C,  and  the  dis- 
crepancy increases  with  the  magnitude  of  the  values  involved.  This 
fact  has  been  accounted  for  in  two  different  ways.  First,  it  may  be 
supposed  that  the  arrangement  of  the  genes  is  really  not  linear,  that 
B  lies  out  of  line  with  A  and  C,  so  that  AC  will  be  less  than  the  sum  of 
AB  and  BC,  and  that  the  more  distant  genes  are  no  farther  apart  than 
indicated  by  the  cross-over  percentages  between  them.  This  ex{)la- 
nation  has  met  with  more  difficulties  than  it  has  cleared  away.  The 
second  explanation  is  that  the  map-distances  indicate  proportionate 
numbers  of  breaks  in  the  linkage  chain  between  points,  not  propor- 
tionate numbers  of  changes  of  relation  between  genes  at  particular 
points.  Thus,  suppose  genes  ABCDE  of  a  linkage  system  meet  their 
allelomorphs,  abcde,  in  a  cross  and  gametes  are  later  formed  by  the 
cross-bred  as  follows,  (i)  ABcde,  (2)  ABcdE,  and  (3)  AbcDe.  Assum- 
ing that  the  arrangement  is  linear,  we  must  suppose  that  one  break 
in  the  linkage  chain  has  occurred  in  (i),  two  breaks  in  (2),  and  three 
breaks  in  (3).  But  if  we  did  not  have  genes  BCD  under  observation, 
and  merely  noted  the  relation  of  A  to  E,  we  should  infer  that  in  case 
(i)  and  in  case  (3)  a  single  crossover  had  occurred.  We  should  on  that 
basis  underestimate  the  amount  of  breaking  in  the  linkage  chain. 
Accordingly  the  construction  of  maps  on  the  basis  of  short  distances 
summated  is  justifiable,  provided  the  arrangement  is  linear,  as  it  seems 
to  be.  But  it  must  be  borne  in  mind  that  the  map  distances  do  not 
correspond  with  cross-over  percentages  (although  they  are  based  on 
them)  except  in  the  case  of  very  short  distances.  Alap  distances  often 
exceed  50,  but  cross-over  percentages  cannot  do  so,  as  already  pointed 
out.  To  get  a  distinctive  name  for  the  map  units,  Haldane  has  called 
them  units  of  Morgan  or  simply  ''morgans."  Haldane  has  computed 
a  formula  for  converting  cross-over  percentages  into  ''morgans"  and 
vice  versa.  He  finds  that  the  two  correspond  only  for  very  low  values 
(5  or  less)  and  diverge  more  and  more  as  the  observed  cross-over  per- 
centages approach  50.  Haldane's  formula  may  be  stated  thus.  If 
three  genes,  A,  B,  and  C,  occur  in  a  common  hnkage  group,  and  ihc 
cross-over  percentages  are  known  between  A  and  B  and  between  B  and 
C,  we  may  predict  with  a  probable  error  of  not  over  2  per  cent,  what 
cross-over  percentage  will  be  found  to  occur  between  A  and  C.  Call- 
ing the  cross-over  percentage  between  A  and  B,  w,  and  that  between 
B  and  C,  n,  the  cross-over  percentage  between  A  and  C  will  lie  between 
(w+n)  and  (m+n  —  inm).  It  will  approach  the  former  for  amounts 
of  5  or  less,  and  the  latter  for  amounts  of  45  or  over.     In  a  useful  table 


444     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

Haldane  shows  the  calculated  map  distances  (morgans)  for  all  cross- 
over percentages  between  5  and  50.  This  table  is  based  on  the  rela- 
tions of  the  genes  observed  in  the  sex-linked  group  of  Drosophila,  but 
it  applies  equally  well  to  the  second  linkage  group  of  Drosophila,  and 
to  a  group  of  three  genes  in  the  plant,  Primula.  Provisionally  it  may 
be  considered  to  be  applicable  generally  to  linkage  systems  in  animals 

and  in  plants. 

TABLE  IV 

A  Table  for  Converting  Cross-Over  Percentages  into  Map  Distances 
("Morgans")  and  Vice  Versa  (After  Haldane) 


Cross-over  percentage 

k 

.   0.0 

5-0 

8.0 

10. 0 

II  .0 

12.0 

13.0 

]Map  distance 

.   0.0 

5-1 

8.2 

10.3 

II. 4 

12.5 

13-6 

14.0 

I5-0 

16.0 

17.0 

18.0 

19.0 

20.0 

21 .0 

22.0 

14.7 

15-9 

17.0 

18. 1 

19-3 

20.5 

21 .7 

22.9 

24.1 

23.0 

24.0 

25.0 

26.0 

27.0 

28.0 

29.0 

30.0 

31.0 

25-3 

26.6 

27.9 

29.2 

30-5 

31-9 

33-3 

34-7 

36.2 

32.0 

33-0 

34 -o 

35-0 

36.0 

37-0 

38.0 

39.0 

40.0 

37-7 

39-3 

40.9 

42.6 

44-3 

46.1 

48.0 

50.0 

52.2 

41.0 

42.0 

43-0 

44 -o 

45 -o 

46.0 

47 -o 

48.0 

49  0 

54-4 

56.8 

59-6 

62.6 

66.0 

70.1 

75-1 

81.9 

930 

49-5 

49-7 

49.8 

49.9 

50.0 

99.2 

109.4 

117. 7 

128. 1 

As  an  example  of  how  the  table  may  be  used  in  predicting  undeter- 
mined linkage  values,  suppose  that  A  is  linked  with  B,  and  B  with  C 
and  that  between  A  and  B  there  are  10  per  cent  of  crossovers.  What 
will  be  the  cross-over  percentage  between  A  and  C  ?  Converting  the 
observed  cross-over  percentages  into  map  distances  with  the  aid  of  the 
table,  we  find  the  distance  AB  to  be  10.3  and  the  distance  BC  to  be 
15.9.  On  the  linear  theory  the  distance  AC  will  equal  either  the  sum 
or  the  difference  of  AB  and  BC,  that  is  will  be  either  26.2  or  5.4. 
Converting  these  distances  into  cross-over  percentages  by  interpola- 
tion in  the  table,  we  find  that  the  cross-over  percentage  between  A  and 
C  should  be  either  23.7  or  5.1,  according  as  the  linear  arrangement  is 
ABC  or  ACB. 

Measurement  of  linkage. — It  will  be  observed  that  as  the  strength 
of  linkage  increases,  the  cross-over  percentage  decreases.  With  a 
cross-over  percentage  of  50,  there  is  no  linkage.  With  a  cross-over 
percentage  of  o,  the  linkage  is  complete,  two  characters  so  related 
behaving  as  allelomorphs.  Accordingly  we  depend  upon  the  observed 
cross-over  percentage  both  for  the  detection  of  linkage  and  for  the 
measurement  of  its  strength.  But  unfortunately  the  linkage  strength 
varies  inversely  as  the  cross-over  percentage.  This  makes  the  cross- 
over percentage  directly  considered,  a  rather  poor  measure  of  linkage 


LINKAGE  AND  CROSSING-OVER  445 

strength.  It  is  really  the  amount  by  which  the  cross-over  percentage 
falls  below  50  that  measures  directly  the  strength  of  linkage.  Thus 
with  cross-over  percentages  of  50,  40,  30,  20,  10,  and  o,  we  should 
have  linkage  strengths  of  o,  10,  20,  30,  40,  and  50.  We  should  then 
have  a  standard  for  measuring  linkage  strength  directly,  on  a 
scale  of  50.  But  as  we  are  more  accustomed  to  grading  on  a  scale  of 
100,  it  seems  preferable  to  double  the  values  indicated  above.  We 
then  have  grades  of  linkage  strength  on  a  scale  of  100,  as  follows: 

Cross-over  Linkage 

Percentage  Strength 

50  O 

40  20 

30  40 

20  60 

10  80 

o  100 

Accordingly,  to  estimate  the  strength  of  linkage  in  a  particular  case, 
we  multiply  by  2  the  difference  between  the  observed  cross-over  per- 
centage and  50. 

But  suppose  the  observed  cross-over  percentage  were  greater  than 
50,  what  then?  Such  an  occurrence  would  not  indicate  linkage,  a 
tendency  of  characters  to  remain  grouped  as  they  were,  but  an  oppo- 
site tendency,  to  assume  new  groupings.  No  such  tendency  has  been 
observed.  If  it  should  be,  it  would  need  a  different  name  and  method 
of  measurement. 

We  may  now  consider  some  further  examples  of  linkage. 

In  the  plant,  Primula  sinensis,  Gregory  observed  the  occurrence 
of  linkage  in  a  group  of  five  characters,  viz., 

Dominant  Recessive 

1.  Short  style  vs.  long  style  (1) 

2.  Magenta  corolla  vs.  red  corolla  (r) 

3.  Tinged  corolla     vs.  full-colored  corolla 

4.  Green  stigma       vs.  red  stigma  (s) 

5.  Pale  stem  vs.  full  red  stem 

Altenburg  later  determined  the  strength  of  the  linkage  existing 
between  three  of  these  five  pairs  of  characters,  viz.,  1,2,  and  4  of  the 
above  list.     His  results  may  be  expressed  in  a  linkage  map  as  follows : 


-    r    s 

34  o  45-6 


The  cross-over  percentage  between  1  and  r  was  found  to  be  34.02, 
between  r  and  s,  11.62.  The  sum  of  these  two,  45.64,  is  the  total 
(uncorrected)  map  distance.     The   observed   cross-over  percentage 


446     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

between  1  and  s  was  40.6,  which  falls  short  of  the  map  distance  by 
almost  exactly  the  amount  indicated  by  Haldane's  table. 

In  the  sweet  pea  the  earliest  discovered  examples  of  linkage  are 
found.  Here  are  known  two  linkage  groups  containing  each  three 
pairs  of  characters  as  follows : 

Dominant  Recessive 

{I.  Blue   VS.  red  flower  color 
2.  Long  vs.  round  pollen 
3.  Erect  vs.  hooded  standard 

(  I.  Dark      vs.  light  leaf-axil 
Group  2  I  2.  Fertile   vs.  sterile  anthers 
3.  Normal  vs.  cretin  flowers 

Results  described  by  Bateson  and  by  Punnett  indicate  that  in  Group  i 
the  map  relations  of  the  three  genes  are : 

E— B L 

0.78  12.5 

The  group  is  a  compact  one,  with  E  and  B  very  closely  linked,  cross- 
over percentage  less  than  one,  with  B  and  L  showing  between  1 1  and 
12  per  cent  crossovers,  and  with  E  and  L  showing  about  12.5  per  cent 
of  crossovers. 

In  Group  2,  the  cross-over  percentage  between  D  and  F  is  about 
6.2,  between  F  and  N  about  25.0.  Until  the  cross-over  percentage 
between  D  and  N  has  been  experimentally  determined,  it  cannot  be 
stated  whether  the  "map"  order  is  FDN  or  END.  In  the  former 
case,  the  total  map  distance  will  be  25,  or  about  double  the  length  of 
Group  I ;  in  the  latter  case,  it  will  be  still  longer,  or  about  31.2. 

In  garden  peas  two  independent  pairs  of  linked  characters  are 
known  and  two  more  are  suspected  (White) .  In  one  of  the  estabhshed 
cases  close  linkage  is  found  between  round  starchy  seeds  and  tendrils 
on  the  leaves,  with  about  1.5  per  cent  of  crossing-over.  In  the  other 
case  a  gene  for  late  flowering  is  linked  with  red  flower  color  with  an 
estimated  cross-over  percentage  of  between  12  and  16. 

In  the  snapdragon,  Antirrhinum,  two  factors  for  flower  color  were 
found  by  Baur  to  be  linked,  with  about  20  per  cent  of  cross-overs  occur- 
ring. 

In  maize  three  linkage  groups  are  known,  one  of  four  factors  and 
two  of  two  factors  each.  Group  i  includes  a  factor  for  waxy  endo- 
sperm and  the  factor  C  for  aleurone  color.  These  show  a  cross-over 
percentage  of  26.7.  Group  2  includes  four  linked  factors,  aleurone 
fa   ctor  R,  chlorophyll  factor  G,  chlorophyll  factor  L,  and  aleurone 


LINKAGE  AND  CROSSING-OVER 


447 


TABLE  V 
Cases  of  Linkage  in  Plants  or  in  Animals  Other  Than  Drosophila 


Species 

a 

3 
O 

li 

O 

I 
I 
I 
2 
2 

2 

I 
2 

I 

I 

2 
2 
2 

3 

I 
2 

I 

I 

I 

I 
I 
I 
I 

I 
I 
I 

I 

I 

I 
I 

I 

Linked  Characters 

Cross-over 
Percentage 

Linkage 
Strength 

Authority 

Sweet  pea 

Purple  flowers,  long  pollen 
Purple  flowers,  erect  standard 
Long  pollen,  erect  standard 
Dark  axil,  fertile  anthers 
Dark  a.xil,  normal  (not  cretin) 

flower 
Fertile  anthers,  normal  (not 

cretin)  flowers 

ri  or  12 
0.78 

12.5 
6.2 

? 

25.0 

76-78! 

98.4 

75 
87.6  , 

50      . 

32 

18.8  • 
76.8, 

Bateson 

and 
Punnctt 

Primula 
sinensis 

Short  style,  magenta  corolla 
Short  style,  green  stigma 
Magenta  corolla,  green  stigma 
Tinged  corolla,  green  stigma 
Pale  stem,  green  stigma 

340 
40.6 
II. 6 

? 

? 

Altenburg 
Gregory 

Garden  pea 

Round     seeds,     tendrils     on 
leaves 

Late  flowering,  colored  flow- 
ers 

1-5 
12-16 

97 
68-76 

Bateson  and 
Vilmorin 

Hoshino 

Antirrhinum 

Red    flower    color,    "pictur- 
atum"  pattern 

20.0 

60 

Baur 

Maize 

Waxy  endosperm,  Aleurone  C 
Aleurone  R,  Chlorophyl  G 
Aleurone  R,  Chlorophyl  L 
Chlorophyl  G,  Chlorophyl  L 
Starchy  endosperm,  tunicate 
seed 

26.7 

19.0 

0.0 

23.0 

8.3 

46.6 
62?   ' 
100 
54      . 

83.4 

Breggar 
Lindstrom 

Jones 

Tomato 

Vine  habit,  fruit  shape 
Green  foliage,  2-celled  fruit 

20.0 
0? 

60      1 
100?   J 

Jones 

Beans 

Seed  pattern,  vine  habit 

0? 

100? 

Surface 

Silkworm 

Pattern   Q   of   larva,   yellow 

silk 

26. 1 

47.8 

Tanaka 

Apotetlix 

Patterns  G  and  M 
Patterns  M  and  K 
Patterns  K  and  Y 
Patterns  Y  and  R 
Patterns  Y  and  T 
Patterns  R  and  T 
Patterns  ]M  and  R 
Patterns  Y  and  Z 

4  (in?; 

I  (in?) 

6  (in?) 
10  (in?) 
12  (in?) 

0  (in?) 
10  (in?) 
10  (in?) 

92 
98 

88 

76 

100 

80 

80 

Nabours 

Pigeon 

Sex-linked  factors  I  and  A 

40  (in<5) 

20 

Cole  and 
KcUey 

Rat 

Albinism,  red-eye 
Albinism,  pink-eye 
Red-eye,  pink-eye 

I.O? 

21 .0 
18.3 

98?! 

58     • 

63-4] 

Castle  and 
Dunn 

Mouse 

Albinism,  pink-eye 

14  3 

71.4 

Castle  and 
Dunn 

448     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

spotting  factor,  S.  No  crossovers  have  been  observed  between  R  and 
L  which  behave  as  if  they  were  allelomorphs,  or  "completely  linked." 
The  cross-over  percentage  between  L  and  G  has  been  determined  as  23, 
that  between  R  and  G  has  been  determined  less  accurately  as  19,  and 
that  between  R  and  S  as  12.5.     The  order  of  the  genes  is  accordingly 

R— L S G. 

Group  3  includes  the  two  characters,  starchy  endosperm  and  tunicate 
("podded")  seeds.  The  cross-over  percentage  in  this  case  is  S.;^ 
(Jones  and  Gallastegui).  • 

In  the  cultivated  tomato  two  cases  of  linkage  have  been  reported. 
A  gene  for  "standard"  vine  habit  and  a  gene  for  '^constricted"  fruit 
shape  show  about  20  per  cent  of  crossing  over.  In  another  linkage 
group,  no  crossovers  have  been  observed  between  green  foliage  color 
and  two-celled  fruit,  as  opposed  to  yellow  foliage  color  and  many- 
celled  fruit,  in  a  total  of  24  F2  plants.  It  seems  probable  that  the 
linkage  in  this  latter  case  is  close,  though  the  number  of  observations 
is  too  small  to  do  more  than  establish  a  probability. 

In  rats  a  group  of  three  linked  characters  has  been  found,  albinism 
(c),  red-eye  (r)  and  pink-eye  (p),  which  may  be  mapped,  thus 


c — r p 

01  20 

In  mice  albinism  (c)  and  pink-eye  (p)  are  linked,  as  they  are  in  rats, 
but  the  cross-over  percentage  is  less,  viz.,  14.3. 

In  the  silkworm,  linkage  occurs  between  a  factor,  Q,  which  gives 
to  the  larva  characteristic  pattern  markings,  and  a  factor,  Y,  which 
gives  to  the  blood  of  the  larva  and  the  silk  of  the  cocoon  a  yellow  color. 
Crossing-over  occurs  only  in  males,  and  in  a  percentage  of  26.1  (in  a 
large  series  of  backcrosses  of  Fi  hybrid  male  with  double  recessive 
female,  producing  24,918  individuals).  In  Drosophila  crossing-over 
occurs  only  in  the  female  parent,  that  is  in  the  maturation  of  the  eggs. 
This  is  true  of  all  linkage  groups,  whether  they  involve  sex-linkage 
or  not.  In  the  grouse-locust,  Apotettix,  a  linkage  group  of  seven  or 
more  characters  has  been  discovered  by  Nabours,  which  have  this 
curious  feature,  that  crossing-over  seems  to  occur  much  more  fre- 
quently in  females  than  in  males.  In  all  other  known  cases  of  linkage, 
crossing-over  occurs  with  about  the  same  frequency  in  the  gametes 
formed  by  both  sexes.  This  accordingly  is  to  be  regarded  as  the 
normal  condition.  Failure  of  crossing-over  to  occur  in  the  oogenesis 
of  Drosophila  and  in  the  spermatogenesis  of  the  silkworm  would  seem 
to  imply  unusual  cytological  conditions  in  those  cases. 


CHAPTER  XXXIII 
SEX  DETERMINATION 

VARIOUS  THEORIES  OF  SEX  DETERMINATION 
H.  H.  Newman 

In  earlier  chapters  it  has  been  necessary  to  introduce  a  few  neces- 
sary facts  about  sex  determination  and  sex-linked  heredity.  The 
mechanism  of  sex  determination  has  been  clearly  described  and  illus- 
trated for  Drosophila  (pp.  411  ff.),  and  the  close  connection  that  exists 
between  sex-linked  heredity  and  sex  determination  has  been  shown  in 
chapters  xxxi  and  xxxii.  A  more  detailed  consideration  of  sex  deter- 
mination and  sex  differentiation  is  now  to  come. 

The  question  as  to  what  determines  whether  an  animal  shall  be  a 
male  or  a  female  is  a  very  ancient  one,  and  it  is  only  during  the  present 
century  that  we  have  solved  the  puzzle. 

A  great  many  theories  of  sex  determination  have  been  proposed, 
some  of  which  are  as  follows: 

a)  Hippocrates  and  some  subsequent  theorists  believed  that  the 
sex  of  the  offspring  depended  on  the  relative  vigor  of  the  parents,  the 
more  vigorous  parent  giving  his  or  her  sex  to  the  offspring. 

h)  Thury  thought  that  the  sex  of  the  offspring  depended  on  the 
degree  of  ripeness  of  the  ovum  at  the  time  of  fertilization. 

c)  Various  writers  claim  that  statistics  show  that  germ  cells  from 
the  right  ovary  produce  males  and  those  from  the  left  ovary  females. 

d)  The  nutrition  theory. — The  egg  is  a  much  more  highly  nourished 
cell  than  the  spermatozoon,  and  the  idea  seems  natural  that  high 
degrees  of  nourishment  of  the  mother  produce  female  offspring  and 
lower  degrees  of  nourishment  male  offspring.  Professor  Schenk  of 
Vienna  gained  a  huge  reputation  by  controlling  the  diet  of  certain 
royal  prospective  mothers  and  predicting  the  sex  of  the  offspring 
accordingly.  He  was  correct  in  his  predictions  several  times,  but  his 
success  was  short-lived.  His  early  predictions  were  merely  lucky, 
just  as  one  might  be  who  could  guess  heads  or  tails  correctly  several 
times  in  succession. 

Some  color  is  lent  to  the  nutrition  hypothesis  by  the  fact,  if  it  is  a 
fact,  that  after  war  or  famine,  when  the  nutrition  of  mothers  has  been 

449 


450      READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

low,  more  males  than  females  are  born.  This  is  probably  a  case  of 
differential  prenatal  mortality.  By  that  we  mean  that  more  females 
die  unborn  than  males,  because  the  latter  are  hardier  and  stand  pre- 
natal malnutrition  better. 

e)  Sex  is  deter?nined  at  the  time  of  fertilization. — Perhaps  the  best 
evidence  that  sex  is  determined  at  the  very  beginning  of  development 
is  derived  from  one-egg  twins  and  quadruplets.  In  the  nine-banded 
armadillo  practically  every  female  gives  birth  to  quadruplets,  four 
essentially  identical  young  being  produced  in  each  litter.  All  in  a 
given  set  of  quadruplets  are  invariably  of  the  same  sex,  either  four 
males  or  four  females.  Newman  and  Patterson  have  shown  that  each 
set  of  quadruplets  comes  from  a  single  egg  which  at  a  very  early  stage 
divides  into  four  parts  to  form  four  foetuses  (Fig.  94).  The  conclusion 
is  that  sex  was  determined  before  the  separation  took  place.  Human 
identical  twins,  also  always  of  the  same  sex,  furnish  further  evidence 
in  favor  of  very  early  sex  determination.  These  and  numerous  other 
similar  facts  justify  the  conclusion  that  sex  is  determined  at  the  time 
of  fertilization. 

THE  CHROMOSOMAL  MECHANISM  OF  SEX  DETERMINATION 

The  well-established  case  of  Drosophila  (pp.  411  ff.)  will  serve  as  a 
basis  for  comparison.  Many  cases  similar  to  that  of  Drosophila  have 
been  worked  out.  The  chief  differences  have  to  do  with  the  X  and  Y 
chromosomes.  Sometimes  the  X  chromosome  is  distinct  and  inde- 
pendent during  synapsis  and  maturation,  but  cases  are  known  in 
which  the  X  chromosome  is  attached  to  the  end  of  one  of  the  ordinary 
chromosomes,  and  will,  of  course,  always  follow  this  chromosome  in 
reduction  division.  The  Y  chromosome  varies  considerably  in  dif- 
ferent species.  Sometimes  the  Y  chromosome  and  the  X  chromosome 
are  optically  indistinguishable.  Sometimes  the  Y  element  is  repre- 
sented by  a  group  of  as  many  as  five  small  chromosomes  which  keep 
together  in  a  group  and  always  go  either  one  way  or  the  other  in  the 
reduction  division.  Again,  the  Y  element  may  be  very  small  or  vesti- 
gial, or,  finally,  it  may  be  wanting  altogether,  so  that  X  is  an  entirely 
unpaired  chromosome  that  goes  to  one  cell  only  at  the  reduction 
division. 

In  spite  of  all  of  these  various  modifications  of  the  X-Y  type  of 
chromosomal  sex-determining  mechanism,  the  method  of  producing 
male-forming  and  female-forming  spermatozoa  is  the  same  in  each 
case.     The  female  gametes  all  have  one  X  chromosome,  while  half  of 


SEX  DETKRMIXATIOM 


451 


the  male  gametes  have  one  X  chromosome  and  the  other  half  have 
no  X,  but  sometimes  Y  and  sometimes  simply  one  chromosome  less 
than  the  first  type  of  male  gametes.     We  can  then  speak  of  the  two 


Fig.  94. — An  armadillo  egg  about  six  weeks  after  fertilization,  showing  the 
quadruplet  foetuses  are  derived  from  the  single  egg  and  all  destined  to  be  of  the 
same  sex.     (Frotn  Newtnan.) 


sexes  produced  by  union  of  male  and  female  gametes  simply  in  terms 
of  the  X  chromosomes,  females  being  characterized  by  XX  (duplex) 
and  males  by  X  (simplex). 


SEX  DETERMINATION  IN  PARTHEXOGENETIC  SPECIES 

Although  it  was  at  first  thought  that  the  facts  of  parthenogenesis 
(development  of  eggs  without  fertilization)  was  opposed  to  the 
chromosomal  mechanism  of  sex  determination,  further  study  of  this 


45^      IIEADINGS  IX  EVOLUTION,  GENETICS,  AND  EUGENICS 

phenomenon  only  served  to  line  up  this  category  of  sex  determina- 
tion with  the  type  already  explained. 

In  the  hees  and  wasps  it  has  long  been  known  that  eggs  which  are 
extruded  without  fertilization  produce  drones  (males),  while  fertilized 
eggs  produce  workers  or  queens  (both  females).  It  has  now  been  dis- 
covered that  the  bee  egg  undergoes  the  reduction  division  before 
fertilization  so  that  all  eggs  will  have  only  one  X  chromosome.  The 
eggs  that  are  fertilized  always  have  the  XX  condition  and  will  produce 
only  females,  while  the  eggs  that  are  not  fertilized  keep  the  X  con- 
dition and  produce  males.  These  males  with  only  half  the  normal 
number  of  chromosomes  cannot  carry  out  the  reduction  division,  but 
produce  spermatozoa  always  with  an  X  chromosome. 

In  aphids  parthenogenetic  individuals  are  always  females  and  in 
this  case  it  has  been  discovered  that  the  egg  develops  without  under- 
going the  reduction  division,  thus  retaining  the  XX  condition. 

In  all  of  the  cases  hitherto  mentioned  the  female  is  said  to  be  homo- 
zygous for  sex,  because  she  produces  gametes  of  only  one  kind,  from 
the  sex  standpoint,  each  matured  egg  having  the  X  chromosome  pres- 
ent. The  male,  on  the  contrary,  is  said  to  be  heterozygous  for  sex 
since  two  kinds  of  sperms  are  produced,  one  with  X  and  the  other  with- 
out X.  The  great  majority  of  animals  appear  to  have  a  similar 
mechanism,  but  there  are  a  few  groups  of  animals  which  are  just  the 
reverse  of  what  we  have  described,  since  the  female  is  heterozygous 
for  sex  and  the  male  homozygous. 

THE  POULTRY  TYPE  OF  SEX  DETERMINATION 

There  is  now  evidence  both  cytological  and  genetic  that  in  poultry, 
and  probably  in  all  birds,  there  are  two  kinds  of  maturated  eggs,  one 
having  the  X  chromosome  and  the  other  with  the  Y  chromosome,  or  at 
least  without  an  X  chromosome.  All  of  the  spermatozoa  are  believed 
to  have  the  X  chromosome.  As  has  already  been  seen  (chapter  xxxi), 
the  sex  linkage  is  just  the  reverse  of  that  seen  in  the  majority  of 
animals  when  the  male  is  the  heterozygous  sex.  Moths  and  butterflies 
are  also  probably  of  the  same  type  as  poultry.  In  the  classic  case 
of  Abraxas,  the  currant  moth,  a  pale  mutant  occurred  which  was 
female  and  was  sex-linked  to  females  just  as  white  eye  color  was 
linked  to  males  in  Drosophila.  Apart  from  the  fact  that  the  XX  con- 
dition seems  to  have  shifted  from  one  sex  to  the  other  in  these  two 
groups  (birds  and  butterflies)  the  mechanism  of  sex  determination 
seems  to  be  exactly  the  same  as  in  the  majority  of  animals  studied. 


SEX  DETKRMIXATIOX  45^ 

SEX    DIFFERENTIATION 

It  now  becomes  necessary  to  distinguish  clearly  between  sex 
determination  and  sex  differentiation.  When  we  say  that  by  means 
of  a  chromosomal  mechanism  sex  is  determined,  exactly  what  do  we 
mean  ?  We  answer  that  the  sex  of  an  individual  arising  from  a  fertil- 
ized egg  (in  the  case  of  parthenogenesis,  an  unfertilized  egg)  has  been 
settled.  Now  as  a  matter  of  fact  only  one  thing  has  been  settled  irrevo- 
cably, and  that  is  that  one  individual  will  have  the  chromosome 
composition  characteristic  of  a  male  and  another  individual  that  of  a 
female.  A  male  is  usually  an  individual  that  produces  spermatozoa 
and  a  female  one  that  produces  ova.  Is  it  irrevocably  settled  beyond 
possibility  of  reversal  that  a  zygote  with  the  XX  chromosome  com- 
position must  produce  eggs  and  one  with  the  X  composition,  sper- 
matozoa ?  This  question  has  apparently  been  answered  by  Geoffrey 
Smith  in  his  work  on  parasitically  castrated  crabs  and  by  Richard 
Goldschmidt  on  Gypsy  moths.  In  the  first  case,  individual  crabs 
whose  testes  had  been  infested  by  the  parasitic  cirripede,  Sa^cidina, 
were  gradually  changed  over  in  their  whole  metabolism  to  such  an 
extent  that  cells  destined  to  produce  spermatozoa  produced  ova.  In 
the  second  case,  when  certain  varieties  of  moth  were  crossed,  all  of 
the  germ  cells  produced  females  with  ova,  whereas  half  of  the  eggs 
had  the  XX  and  half  the  X  chromosome  content.  This  evidently 
means  that  some  individuals  with  the  male  chromosome  character 
produced  eggs.  From  these  results  we  may  be  justified  in  conclud- 
ing that  not  even  this  most  fundamental  difference  of  sexes,  that  of 
the  female  producing  ova  and  the  male  spermatozoa,  is  irrevocabh' 
predetermined  at  fertilization. 

Lest  the  reader  be  confused,  however,  we  hasten  to  add  that  under 
natural  conditions  of  life  an  individual  with  the  male  chromosomal 
content  produces  spermatozoa  and  one  with  the  female  chromosomal 
content  produces  eggs,  and  that  only  rare  accidental  or  unnatural 
conditions  disturb  the  normal  course  of  events.  For  purj:)oses  of 
practical  genetics  we  may  then  define  a  female  as  an  individual  that 
produces  ova  and  a  male  as  one  that  produces  spermatozoa. 

Secondary  sexual  characters. — Usually  males  and  females  differ 
from  each  other  in  many  other  characters  besides  the  production  of 
eggs  or  sperm.  Often  one  sex  is  larger,  stronger,  more  elaborately 
ornamented  and  colored  than  the  other  and  possesses  characteristic 
accessory  sex  organs  whose  function  it  is  to  facilitate  the  bringing 
together  of  the  eggs  and  the  sperm.     All  of  the  differences  between  the 


454     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

sexes  other  than  the  primary  difference  of  egg  or  sperm  production  are 
called  secondary  sexual  characters.  Usually  very  young  animals  show 
only  slight  differences  in  secondary  sexual  characters  and  the  differ- 
ences increase  markedly  at  sexual  maturity.  We  speak  of  the  gradual 
divergent  development  of  the  two  sex  types  as  sex  differentiation. 
The  question  arises  as  to  whether  or  not  the  chromosomal  differences 
are  the  causes  of  the  differentiation  of  secondary  sexual  characters. 
These  secondary  sexual  characters  are  all  somatic,  and,  since  the  soma 
is  the  product  of  cell  division  of  the  zygote,  the  soma  cells  must  have 
either  the  male  or  the  female  chromosomal  character.  That  the 
chromosomal  mechanism  in  the  somatic  cells  is  not  sufficient  of  itself 
to  bring  about,  unaided,  the  differentiation  of  secondary  sexual  charac- 
ters can  be  shown  readily  in  at  least  many  animals. 

In  the  mammals,  for  example,  it  is  known  that  the  early  removal 
of  the  testes  or  ovaries  results  in  a  retention  of  the  juvenile  or  undif- 
ferentiated condition  of  secondary  sexual  characters.  Evidently  some 
influence  is  exerted  by  the  tissues  of  the  gonad  that  is  necessary  for  the 
full  differentiation  of  sex  characters.  The  current  theory  is  that 
certain  glandular  cells  that  form  part  of  the  body  of  ovary  or  testes 
excrete  materials  into  the  blood  that  stimulate  various  tissues  in 
different  ways  and  produce  dimorphic  results.  The  specific  sub- 
stances produced  by  these  glands  are  called  "hormones,"  for  want 
of  a  better  name.  To  test  the  efficiency  of  these  hormones  the  crucial 
experiment  of  taking  out  the  gonads  of  a  young  rat  or  guinea  pig  and 
implanting  the  gonad  of  an  individual  of  the  opposite  sex  has  been 
many  times  performed.  For  example,  Steinach  castrated  young  male 
rats  and  then  successfully  grafted  into  them  ovaries  from  young 
female  rats.  The  result  was  that  these  young  rats  which  started  to 
be  males  became  much  altered  in  a  female  direction,  the  mammary 
glands  becoming  greatly  enlarged,  their  instincts  more  feminine  than 
masculine,  and  in  a  number  of  other  particulars  they  showed  more 
or  less  pronounced  evidences  of  feminization.  Conversely,  spayed 
females  with  engrafted  testes  showed  a  tendency  toward  male  differ- 
entiation, especially  in  instincts.  These  experiments  have  been 
largely  confirmed  by  C.  R.  Moore. 

Similar  experiments  with  similar  results  have  been  performed 
with  fowls  and  ducks.  All  indicate  that  the  glandular  part  of  the 
gonads  has  a  determinative  effect  on  sex  differentiation,  and  this  in 
spite  of  the  chromosome  make-up  of  the  somatic  cells;  for  the  male 
differentiation  in  cells  with  the  male  chromosome  characters  can  be 


SEX  DETKRMLvvTrON 


455 


456      READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

inhibited  and  female  differentiation  superimposed  if  the  female  gonad 
is  introduced  in  the  absence  of  the  male  gonad. 

A  beautiful  experiment  conducted  by  nature  herself  helps  to  drive 
home  the  hormone  theory  of  sex  differentiation.  In  cattle,  as  shown 
recently  by  F.  R.  Lillie,  twins  occur  in  a  small  percentage  of  cases  and 
involve  the  simultaneous  fertilization  of  two  eggs.  These  eggs  lie  as 
a  rule  in  opposite  horns  of  the  forked  uterus,  but  owing  to  the  growth 
of  their  embryonic  membranes  the  two  individuals  come  to  fuse  cir- 
culations so  that  there  is  an  admixture  of  blood  (Fig.  95).  The  result 
is  that  if  the  twins  are  zygotically  of  the  same  sex,  no  untoward  effect 
of  blood  admixture  is  apparent,  but  when  the  twins  are  zygotically  a 
male  and  a  female,  the  female  individual  is  always  stopped  in  its 
female  differentiation  and  becomes  more  or  less  completely  trans- 

* 

formed  in  a  male  direction.  It  appears,  however,  that  at  the  time 
when  blood  admixture  occurs,  the  female  individual  has  already 
differentiated  so  far  with  respect  to  the  external  genitalia  and  in  other 
respects  that,  even  though  subsequent  development  be  entirely  male 
in  character,  the  resultant  individual  is  always  a  sterile  creature, 
neither  fully  a  female  nor  a  complete  male.  Such  individuals  have 
long  been  known  as  "  freemartins."  As  a  rare  exception  to  the  general 
rule  an  occasional  case  has  appeared  in  which  a  male  and  a  female  pair 
fail  to  undergo  blood  admixture.  In  such  cases  both  develop  into 
normal  animals.  It  now  appears  that  the  reason  why  the  female  sex 
is  the  one  to  suffer  is  that  the  male  gonads  differentiate  precociously, 
before  the  female,  and  inhibit  the  subsequent  development  of  female 
gonads.  Hence  the  only  hormones  in  the  blood  of  both  twins  are 
the  male  hormones. 

In  conclusion  we  may  say  then  that  though  chromosoines  tend 
to  determine  the  primary  sex  differences,  they  have  no  effect  on  the 
differentiation  of  secondary  sexual  characters.  These  are  due  to 
substances  secreted  by  the  gonads  that  has  been  called  a  hormones. 


PART  V 
EUGENICS 


CHAPTER  XXXIV 

THE  INHERITANCE  OF  HUMAN  CHARACTERS, 
PHYSICAL  AND  MENTAL^ 

ELLIOT   R.    DOWNING 

Anyone  who  undertakes  to  trace  the  ancestry  of  an  individual  is 
soon  impressed  with  the  fact  that  it  is  a  difficult  task  even  to  find  the 
names  of  the  persons  involved  three  or  four  generations  back;  it  is 
much  more  difficult  to  determine  with  certainty  their  physical  and 
mental  characteristics.  One  can  more  surely  find  the  pedigree  of  a 
horse  or  hog  that  he  may  own  than  he  can  of  a  child  in  whom  he  is 
interested,  for  we  do  have  registry  books  for  good  stock,  but  none 
ordinarily  for  human  family  relations  (in  Illinois  not  even  compulsory 
birth  registrations  until  very  recently),  so  that  a  child  born  in  this 
state  may  not  even  legally  prove  his  existence  or  parentage  by  official 
records.  It  is  not  an  easy  matter,  therefore,  to  find  human  data  that 
illustrate  the  various  phases  of  heredity  concerning  which  we  are 
reasonably  sure  in  dealing  with  animals  and  plants. 

Fortunately,  there  are  some  studies  of  the  inheritance  of  physical 
characters  that  are  quite  satisfactory.  There  is  an  increasing  number 
of  studies  of  the  inheritance  of  insanity,  feeble-mindedness,  epilepsy, 
and  alcoholism  by  the  scientific  staff  of  institutions  deahng  with  such 
cases,  and  we  do  have  a  fairly  good  mass  of  material  in  the  lines  of 
descent  of  the  royal  families  of  Europe,  where  the  matings  and  the 
characters  of  the  individuals  are  more  or  less  matters  of  history. 
Thanks  to  the  generosity  of  some  men  of  wealth  and  foresight,  appre- 
ciative of  the  importance  of  a  better  knowledge  of  the  laws  of  human 
heredity,  we  have  in  several  countries  well-endowed  laboratories  with 
expert  staffs  founded  on  purpose  to  study  this  topic;  such  as  the 
Galton  Laboratory  of  Eugenics  in  England  and  the  Eugenics  Labora- 
tory of  the  Carnegie  Institution,  Cold  Springs  Harbor,  New  York. 

Occasionally  a  family  is  found  in  which  one  or  more  members  have 
five  fingers  instead  of  four;  such  a  condition  is  known  as  polydactyl- 
ism.     Sometimes  a  case  is  recorded  in  which  a  person  has  fingers  with 

^  From  E.  R.  Downing,  The  Third  atid  Fourth  Generation  (The  University  of 
Chicago  Press,  copyright  1920). 

459 


46o     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

two  joints  instead  of  three  and  a  thumb  with  one  joint  in  place  of  two 
(brachydactyUsm).     Such  human  abnormahties  are  inherited.     There 


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is  given  on  this  page  a  chart  (Fig.  96)  of  a  family  tree  in  which 
brachydactylism  is  very  common;  it  is  based  on  a  study  made  by 
Drinkwater.     Males  in  the  chart  are  represented  by  6,  females  by  ?, 


INHERITANCE  OF  HUMAN  CHARACTERS 


461 


matings  by  = .  The  circles  are  of  solid  color  •  in  individuals  afTccted 
with  the  deformity,  open  O  in  normal  individuals.  The  character 
seems  to  behave  like  a  Mendelian  dominant,  though  one  could  make 
no  very  positive  assertion  on  this  point  from  so  few  individuals.  Hut 
it  is  very  evident  that  such  a  physical  character  once  in  the  stock  is 
transmitted  generation  after  generation,  reappearing  continually  in 
the  offspring. 

Below  there  is  presented  a  chart  (Fig.  97)  of  the  transmission 
of  cataract.  This  disease  is  characterized  by  the  aj^pearance  of 
an   opaque   area   in    the    usually    transparent   parts    of    the    eye, 


f       I 1 1 r 


4  ^  €  4  f         99         fxd'x9 


99(D(S)ff     ®® 


®®  o©  o  909    4     f  • 

9     ®4Q)f^(5 

Fig.  97. — Inheritance  of  one  form  of  cataract.  Modified  from  Nettleship's 
chart.  The  diagram  reads  thus:  A  man  with  cataract  married  a  normal  woman; 
of  their  eight  children  six  were  affected  with  the  disease.  One  of  these  married 
an  unaffected  man;  three  of  the  children  of  this  union  were  normal,  sex  unrecorded, 
two  defective.  This  same  man  married  a  second  wife  who  was  normal;  their 
eight  children  were  all  unaffected.  So  continue  reading  through  five  generations. 
{From  Downing.) 


ultimately  rendering  the  person  blind.  In  the  particular  form 
of  the  disease  here  considered  it  does  not  develop  until  middle 
life.  Clarence  Loeb  in  a  study  of  hereditary  blindness  pul^lished 
in  1909  tabulated  the  results  of  a  study  of  304  families  in  which 
such  blindness  occurs.  There  were  1,012  children,  of  whom  58  per 
cent  were  affficted,  which  is  about  the  percentage  expected  when 
hybrid  defectives  mate  with  normal  individuals  and  the  defect  is  a 
dominant  character.  Similar  extensive  studies  of  congenital  deafness 
and  deaf-mutism  show  that  these  are  similarly  heritable,  though  just 
how  the  character  behaves  is  not  yet  known,  for  undoubtedly  under 
"deafness"  are  included  a  variety  of  diseased  conditions  that  must  be 


462      READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

studied  separately  before  we  shall  know  how  each  is  inherited.  Care 
must  be  taken,  too,  to  distinguish  between  congenital  deafness  and 
blindness — that  which  inheres  in  the  germ  plasm — and  those  forms, 
due  to  accident  or  contagious  disease,  which  are  acquired  modifications 
and  so  not  heritable.  Thus  measles  often  produces  deafness  as  one 
of  its  after  effects.  Persons  so  rendered  deaf  would  not  transmit  the 
affliction  to  their  children  any  more  than  they  would  transmit  blind- 
ness if  the  eyes  of  the  parents  were  put  out  by  accident. 

Feeble-mindedness  apparently  behaves  as  a  Mendelian  recessive. 
Goddard's  studies  of  the  family  pedigree  of  the  inmates  of  the  Vine- 
land,  New  Jersey,  institution  for  the  care  of  the  feeble-minded  gives 
us  an  abundance  of  material  to  show  the  heritability  of  this  defect  and 
its  relation  to  alcoholism,  insanity,  syphilis,  etc.  Briefly,  syphilitic 
infection  is  a  fairly  common  cause  of  feeble-mindedness  in  children. 
There  is  a  higher  percentage  of  feeble-mindedness  in  the  offspring 
of  alcoholic  parents  than  among  those  of  parents  not  addicted  to  it. 
There  seems  little  or  no  causal  relation  between  feeble-mindedness 
and  insanity.  But  aside  from  feeble-mindedness  that  may  be  pro- 
duced by  such  causes  or  by  occasional  accidents  such  as  falls, 
blows  on  the  head,  there  is  the  great  mass  of  feeble-mindedness  that 
is  wholly  a  matter  of  heredity. 

If  a  feeble-minded  individual  comes  from  parents  both  of  whom 
are  congenitally  feeble-minded  or  who  both  have  a  great  deal  of  feeble- 
mindedness in  their  ancestry,  such  a  one  is  taken  to  be  a  pure  recessive 
as  far  as  this  character  is  concerned,  and  his  germ  cells  have  a  double 
dose  of  the  factor  for  feeble-mindedness  (FF).  When  two  such  per- 
sons mate,  their  offspring  would  be  expected  to  be  all  feeble-minded, 
for  all  eggs  and  sperm  contain  the  factor  F,  and  when  any  egg  is  fertil- 
ized the  person  produced  is  an  FF  individual.  Out  of  144  such  mat- 
ings  resulting  in  482  offspring  whose  records  are  known,  Goddard 
found  that  476  were  feeble-minded.  This  type  of  mating  as  well  as 
others  cited  below  are  illustrated  in  the  family  pedigrees  shown  on 
pages  463  and  464,  selected  from  Goddard's  book. 

If  a  person  comes  from  parents  one  of  whom  is  entirely  normal  and 
one  is  feeble-minded  with  many  feeble-minded  ancestors,  it  is  probable 
that  such  an  individual  is  a  hybrid  with  germ  cells  that,  as  far  as  this 
one  character  is  concerned,  can  be  designated  NF.  Such  a  person 
will  pass  for  normal,  since  feeble-mindedness  is  recessive.  If  such  a 
one  mates  with  the  type  described  above  (FF),  it  would  be  expected 
that  half  the  offspring  would  be  normal,  half  feeble-minded.     Out  of 


INHERITANCE  OF  HUMAN  CHARACTERS        463 

122  such  matings  producing  371  children,  193  were  found  to  be  feeble- 
minded, 178  normal,  which  is  remarkably  close  to  expectation  con- 
sidering the  diflficulty  of  determining  with  certainty  the  real  character 
of  the  parents.  When  two  individuals  of  the  NF  type  mate,  their 
offspring  would  be  expected  to  give  3  normals  to  i  feeble-minded. 
Out  of  146  children  produced  by  t^t,  such  matings  Goddard  found  39 
were  feeble-minded. 

The  first  of  Goddard's  charts  (Fig.  98)  illustrates  the  family  tree 
of  Gertie  K.,  a  girl  of  12  years,  with  the  mental  development  of  a  child 
of  7.  Males  in  this  and  the  following  chart  are  represented  by  squares, 
females  by  circles.  Note*  that  this  girl  has  a  feeble-minded  brother 
and  that  both  her  parents  are  feeble-minded  and  see  the  appalling 
array  of  feeble-minded  cousins,  aunts,  uncles,  and  other  relatives. 
Her  grandmother  passed  for  a  normal  individual,  although  it  would 
seem  from  her  children  she  must  have  been  an  NF  individual.     The 


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Fig.  98. — Family  of  Gertie  K.     {From  Downing,  after  Goddard.) 

second  chart  (Fig.  99)  is  quite  exactly  Mendelian,  if  we  suppose  the 
grandparents  were  NF  individuals.  This  case  is  particularly  interest- 
ing, for  the  parents  of  these  six  feeble-minded  children  were  high-grade 
morons,  both  immigrants.  The  public  must  support  the  children 
because  we  have  as  yet  instituted  no  expert  examinations  to  detect 
such  defectives  among  our  immigrants  in  order  to  refuse  them  admis- 
sion to  this  country. 

See  what  a  single  unfortunate  alliance  can  produce.  A  young 
man  to  whom  Goddard  gives  the  fictitious  name  of  Martin  Kallikak 
had  children  by  a  feeble-minded  girl  in  the  days  before  the  Civil  War. 
There  have  been  traced  some  480  descendants  from  this  mating,  and 
all  of  them  are  below  normal  intelligence.  Later  this  same  man 
married  a  good  Quaker  girl,  and  496  of  the  descendants  of  this  marriage 
have  been  traced,  all  of  normal  mentality.  The  contrast  is  strikingly 
instructive,  for  the  conditions  are  almost  those  demanded  by  a  scien- 
tific demonstration. 


464     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 


Such  cases  as  those  cited  are  interesting  from  the  standpoint  of  the 
student  of  heredity.  They  are  tremendously  significant  to  the  average 
citizen  because  there  is  in  the  United  States  a  very  large  feeble-minded 
population,  estimated  at  200,000,  nine-tenths  of  whom  are  at  large, 
free  to  reproduce  their  kind,  and  very  prone  to  interbreed,  because  the 
feeble-minded  are  seldom  sought  as  legitimate  mates  by  persons  of 
normal  mentality.  The  number  of  feeble-minded  is  apparently 
increasing  much  more  rapidly  than  the  general  population.  How 
rapidly,  it  is  impossible  to  determine,  for  we  have  no  exact  data  on 
the  number  of  feeble-minded;  we  are  not  yet  awake  to  the  enormity 
of    the  problem  involved.     From   these  feeble-minded  come   some 


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Fig.  99. — Family  of  Charlie  M.     {From  Downing,  after  Goddard.) 


40  per  cent  of  our  prostitutes,  a  fourth  of  our  criminals,  and  at  least  a 
half  of  the  inmates  of  our  almshouses. 

A  generation  ago  the  valley  of  Aosta,  in  Northern  Italy,  was  over- 
run with  feeble-minded  and  idiotic  individuals  of  the  type  known  as 
cretins.  It  was  estimated  that  fully  60  per  cent  of  the  population 
were  affected  with  this  abnormality.  A  law  was  passed  and  enforced 
segregating  the  really  irresponsible  cases  and  prohibiting  the  marriage 
of  cretin  with  cretin.  Now  the  condition  has  almost  disappeared,  and 
it  is  estimated  that  only  a  very  small  percentage  of  the  population  are 
cretins,  these  nearly  all  old,  so  that  this  particular  form  of  idiocy  will 
there  very  soon  be  a  thing  of  the  past.  It  seems  only  a  rational  proce- 
dure to  accomplish  at  least  a  segregation  of  feeble-minded  in  this 


INHERITANCE  OE  HUMAN  CHARACTERS 


465 


country,  even  if  no  more  drastic  action  is  taken.  Otherwise  the  group 
is  bound  to  be  an  increasing  burden  on  the  community,  adding  con- 
stantly to  the  tax  needed  for  their 
support. 

Investigations  of  competent 
officials  in  the  employ  of  insane  hos- 
pitals have  accumulated  a  mass  of 
evidence  demonstrating  the  herit- 
ability  of  many  forms  of  nervous 
diseases  which  most  commonly 
behave  as  recessives.  Rosanoff  and 
Orr,^  in  a  study  of  206  matings 
between  individuals  from  more  or 
less  insane  stock,  found  1,097 
children,  146  of  whom  died  in 
childhood.  There  were  351  afflicted 
offspring  to  586  normal.  The  theoretical  expectations,  knowing  with 
more  or  less  certainty  the  character  of  the  parents,  were  359  to 
578.  There  are  presented  (Figs.  100,  loi)  two  typical  family  pedi- 
In  the  first  an  insane  man  was  twice  married,  each  time  to  an 


riji^£:i^i~^ 


Fig.  100. — (i)  Ignorant,  ''queer"; 
(2)  Insane,  was  in  sanitarium,  com- 
mitted suicide;  (3)  eccentric,  violent 
temper,  ideas  of  persecution  against 
neighbors;  (4)  eccentric,  not  well  bal- 
anced; (5)  alcoholic,  lazy,  indolent; 
(6)  dementia  praecox,  paranoid,  in 
state  hospital;  (7)  violent  temper, 
queer,  extreme  dolichocephaly;  (8) 
defective,  cranial  malformation;  (9) 
inferior,  "slow."  {From  Do'd^ning, 
after  Rosanoff  afid  Orr.) 


grees. 


[ti  d)  (t) 


1 


4  6,4 .iti] 


Fig.  ioi. — (i)  epileptic;  (2)  insane  for  a  time,  recovered;  (3)  epileptic,  imbecile; 
(4)  imbecile;  (5)  melancholy  in  early  married  life,  recovered;  (6)  insane  five 
years,  was  in  state  hospital,  recovered;  (7)  insomnia,  neuralgia;  (8)  daughter  had 
spells  of  excitement;  (9)  feeble-minded;  (10)  dementia  praecox,  katatonic,  in 
state  hospital;  (11)  died  of  marasmus,  had  one  convulsion.  {From  Downing, 
after  Rosanoff  and  Orr.) 

eccentric  woman,  undoubtedly  mildly  insane.  All  the  offspring  were 
unbalanced.  In  the  second  case,  those  distinctly  neurotic  are  indi- 
cated in  soHd  color;  those  having  a  neurotic  element  in  the  germ 
material  are  shaded.  It  might  seem  as  if  insane  individuals  would 
scarcely  add  materially  to  the  general  population,  since  they  are  com- 
monly in  asylums.     Often,  however,  the  inherited  insanity  does  not 


^Eugenics  Record  Office  (Cold  Springs  Harbor,  N.Y.)  Bulletin  No.  5,  191 1. 


466     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

manifest  itself  until  past  middle  life,  when  they  have  already  married 
and  started  a  family.  Moreover,  those  hybrid  individuals  in  whom 
the  insane  tendency  is  present  alongside  of  the  normal  determiner 
appear  as  normal  individuals.  Frequently  they  can  be  detected  only 
by  an  examination  of  the  pedigree.  If  such  individuals  mate,  one- 
fourth  of  the  offspring  would  be  expected  to  be  insane. 

Early  modern  European  history  centers  about  the  doings  of  a 
few  great  men  and  women.  Peter  the  Great  of  Russia,  Ferdinand  and 
Isabella  and  Charles  V  of  Spain,  Frederick  the  Great  of  Prussia,Gusta- 
vus  Adolphus  and  Charles  XII  of  Sweden,  are  among  the  most  brilhant 
of  these  potent  individuals  that  shaped  the  destinies  of  Europe  during 
this  period.  It  is  interesting  to  note  how  their  characters  are  deter- 
mined (and  through  them  national  destinies  are  apparently  decided 
in  no  small  measure)  by  the  hereditary  concentration  of  ability  due 
to  lucky  royal  matings,  and  how  their  genius  is  dissipated  by  unwise 
matings. 

Peter  the  Great  of  Russia  came  as  a  brilliant  type  from  a  good 
stock,  though  with  a  very  evident  taint  of  epilepsy  and  feeble- 
mindedness. He  himself  was  an  epileptic.  His  father,  grandfather, 
and  great-grandfather  had  been  men  of  large  ability.  They  had  married 
peasant  girls,  as  was  the  custom  of  the  czars.  Peter's  own  brothers 
and  sisters  were  in  no  way  remarkable.  His  half-sister  Sophia  was  a 
woman  of  marked  ability,  although  two  of  her  brothers  were  imbeciles, 
one  also  an  epileptic.  As  will  be  seen  from  the  pedigree,  the  epilepsy, 
inbecility,  and  mediocrity  appear  in  both  Peter's  children  and  grand- 
children, as  well  as  in  those  of  his  imbecile  half-brother,  Ivan.  It  is 
interesting  to  note  from  the  pedigree  that  the  feeble-mindedness  and 
epilepsy  seem  to  cling  to  the  males  quite  persistently.  The  females 
of  the  family  are  much  more  apt  to  be  brilliant  and  virtuous.  Peter 
the  Great's  own  son  Alexis  was  a  poor  dissolute  specimen,  and  although 
he  married  Charlotte,  the  angelic  daughter  of  a  great  line,  the  house 
of  Brunswick,  the  son  of  this  mating  was  Peter  II,  of  unstable  mind, 
while  the  daughter  Natalia  was  as  sweet  as  she  was  energetic. 

Isabella  and  Ferdinand  were  both  descendants  from  lines  of  very 
great  individuals,  although  in  each  case  there  is  insanity  in  the  family. 
Isabella  herself  comes  from  an  insane  mother  and  an  imbecile  father, 
but  her  grandparents  and  great-grandparents  were  well-balanced  and 
able.  The  data  for  the  charts  of  these  royal  families  were  taken 
largely  from  F.  A.  Woods's  Mental  and  Moral  Heredity  in  Royalty ^ 
supplemented  with  information  from  other  sources.     He  grades  the 


INHERITANCE  OF  HUMAN  CHARACTERS 


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INHERITANCE  OF  HUMAN  CHARACTERS  469 

individuals  on  a  scale  of  10.  Ten  represents  very  high  aijilitv,  as 
determined  by  the  comparative  amount  of  space  and  laudation  given 
to  the  individual  in  such  standard  works  as  Lippincott's  Biographical 
Dictionary.  Five  out  of  eight  of  Isabella's  great-grandi)arents  rank 
very  high.  John  the  Great  of  Portugal,  twice  her  great-grandfather, 
has  a  grade  of  10.  John  of  Gault,  twice  her  great-grandfather,  has  a 
grade  of  8,  as  does  also  John  of  Castile,  while  Henry  III  of  Castile,  one 
of  her  grandparents,  is  designated  the  model  king.  Ferdinand  I  of 
Aragon,  the  grandfather  of  Ferdinand,  is  a  brother  of  this  same 
Henry  HI  of  Castile,  and  is  also  an  exceedingly  able  king.  Of  the 
children  of  Ferdinand  and  Isabella,  most  were  mediocre  or  distinctly 
inferior.  Joanna  was  insane.  In  the  next  generation,  however,  appears 
Charles  V,  whose  reign  marked  the  acme  of  Spain's  greatness,  partially 
due  to  his  own  abihty,  partially  due  to  the  momentum  of  those  move- 
ments that  were  instituted  by  his  illustrious  grandparents.  Charles  V 
married  his  own  cousin,  as  did  also  John  III.  Children  of  these  two 
matings  married,  and  Don  Carlos,  child  of  this  latter  marriage,  was 
madly  depraved  and  cruel. 

When  insanity  and  briUiancy  are  found  in  the  ancestry  it  seems 
merely  a  matter  of  chance  as  to  whether  the  determiners  for  greatness 
will  be  thrown  together  in  the  union  of  sperm  and  egg  or  those  for 
insanity..  We  can  predict  with  some  certainty, that,  in  a  large  number 
of  offspring,  ability  will  reappear  and  insanity  will  reappear,  but  just 
what  individual  each  will  strike  it  is  impossible  to  prophesy  without 
knowing  much  more  definitely  the  nature  of  the  germ  plasm  involved. 
One  may  say  that  the  convergence  of  a  number  of  lines  of  descent  from 
great  ancestors  toward  one  individual  makes  it  probable  that  he  will 
be  exceptionally  able. 

This  is  nowhere  better  illustrated  than  in  the  family  tree  of 
Frederick  the  Great  of  the  Prussian  house  of  Hohenzollern,  as  will  be 
seen  from  the  chart  on  page  470.  Of  his  great-grandparents,  three 
scale  10,  one  9,  one  8,  two  7,  and  one  6.  Not  one  is  below  mediocrity, 
and  the  majority  are  of  very  high  grade.  Of  his  fourteen  ancestors 
back  three  generations,  only  one  is  distinctly  inferior.  Of  his  brothers 
and  sisters,  four  are  distinctly  great,  three  mediocre,  and  one  inferior. 

It  is  interesting  to  trace  the  efifect  of  the  mating  of  such  sjilendid 
stock  with  another  brilliant  line,  that  of  the  Swedish  royal  house. 
Gustavus  I,  or  Gustavus  Vasa,  is  another  instance  of  the  brilliant 
mutant,  with  some  taint  of  neurosis.  He  married  a  gentle  and  tactful 
princess;  their  son  Charles  IX  was  a  very  able  man,  although  of  their 


470     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 


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472      READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

three  other  children  one  was  insane  and  two  weak.  The  children  of 
Charles  IX  were  both  remarkably  able.  The  daughter  Catherine 
becomes  the  mother  of  a  later  succession  of  kings.  Her  son  Charles  X 
and  his  son  Charles  XI  were  rather  mediocre;  but  Charles  XI,  with 
this  fine  stock  behind  him,  married  Ulrica  Eleanor  (7),  granddaughter 
of  Christian  IV  of  Denmark,  the  most  brilliant  of  all  Danish  sovereigns, 
and  Charles  XII,  their  son,  is  pronounced  by  Voltaire  the  most 
remarkable  man  who  ever  existed.  Charles  XII  had  no  children: 
the  succession  passed  to  his  sister's  son,  Adolph  Frederick  of  Holstein- 
Gottorp,  who  married  Louisa  Ulrica,  sister  of  Frederick  the  Great 
of  Prussia.  The  result  of  this  union  of  two  great  lines  of  hereditary 
ability  was  Gustavus  III,  a  fit  successor  of  Gustavus  Vasa,  Gustavus 
Adolphus,  and  Charles  XII;  he  was  "  a  prodigy  of  talents,"  statesman, 
poet,  dramatist. 


CHAPTER  XXXV 
HUMAN  CONSERVATION^ 

HERBERT   E.    WALTER 
I.      HOW   MANKIND   MAY   BE   IMPROVED 

There  are  two  fundamental  ways  to  bring  about  human  better- 
ment, namely,  by  improving  the  individual  and  by  improving  the  race. 
The  first  method  consists  in  making  the  best  of  whatever  heritage 
has  been  received  by  placing  the  individual  in  the  most  favorable 
environment  and  developing  his  capacities  to  the  utmost  through 
education.  The  second  method  consists  in  seeking  a  better  heritage 
with  which  to  begin  the  life  of  the  individual.  The  first  method  is 
immediate  and  urgent  for  the  present  generation.  The  second  method 
is  concerned  with  ideals  for  the  future,  and  consequently  does  not 
usually  present  so  strong  an  appeal  to  the  individual. 

The  first  is  the  method  of  euthenics,  or  the  science  of  learning  to 
live  well.  The  second  is  eugenics,  which  Galton  defines  as  ''  the  science 
of  being  well  born." 

These  two  aspects  of  human  betterment,  however,  are  inseparable. 
Any  hereditary  characteristic  must  be  regarded,  not  as  an  independent 
entity,  but  as  a  reaction  between  the  germplas7n  and  its  environment. 
The  biologist  who  disregards  the  fields  of  educational  endeavor  and 
environmental  influence,  is  equally  at  fault  with  the  sociologist  who 
fails  sufficiently  to  realize  the  fundamental  importance  of  the  germ- 
plasm. 

Without  euthenic  opportunity  the  best  of  heritages  would  never 
fully  come  to  its  own.  Without  the  eugenic  foundation  the  best 
opportunity  fails  of  accomplishment.  The  euthenic  point  of  view, 
however,  must  not  distract  the  attention  now,  for  the  present  chapter 
is  particularly  concerned  with  the  program  of  eugenics. 

2.      MORE   FACTS   NEEDED 

Since  the  point  of  attack  in  human  heredity  must  be  largely 
statistical,  it  is  of  the  first  importance  to  collect  more  facts.  Our 
actual  knowledge  is  confused  with  a  mass  of  tradition  and  opinion, 

I  From  H.  E.  Waher,  Genetics  (copyright  1913).  Used  by  special  permission 
of  the  publishers,  The  Macmillan  Company. 

473 


474     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

much  of  which  rests  upon  questionable  foundations.  The  great 
present  need  is  to  learn  more  facts;  to  sift  the  truth  from  error  in  what 
is  already  known;  and  to  reduce  all  these  data  to  workable  scientific 
form.  Much  progress  is  being  made  in  this  direction,  owing  to  the 
impetus  given  by  the  revival  of  Mendel's  illuminating  work,  but  as  yet 
the  science  of  eugenics  is  in  its  infancy. 

The  most  systematic  and  effective  attempt  in  this  country  to 
collect  reliable  data  concerning  heredity  in  man  has  been  initiated  by 
the  Eugenics  Section  of  the  American  Breeders'  Association  under  the 
secretaryship  of  Dr.  C.  B.  Davenport.  In  1910  the  Eugenics  Record 
Office,  with  a  staff  of  expert  field  and  office  workers  and  an  adequate 
equipment  of  fire-proof  vaults,  etc.,  for  the  preservation  of  records, 
was  opened  at  Cold  Spring  Harbor,  Long  Island,  New  York,  with 
Mr.  H.  H.  Laughlin  as  superintendent.  "The  main  work  of  this 
office  is  investigation  into  the  laws  of  inheritance  of  traits  in  human 
beings  and  their  application  to  eugenics.  It  proffers  its  services  free 
of  charge  to  persons  seeking  advice  as  to  the  consequences  of  pro- 
posed marriage  matings.  In  a  word,  it  is  devoted  to  the  advance- 
ment of  the  science  and  practice  of  eugenics."  The  publication  of 
results  from  the  Eugenics  Record  Office  has  already  been  begun. 

The  Volta  Bureau,  founded  about  twenty-five  years  ago  in 
Washington  by  Dr.  Alexander  Graham  Bell,  is  collecting  data  with 
reference  to  deafness  and  has  now  systematically  arranged  particu- 
lars concerning  the  history  of  over  20,000  individuals.  In  England, 
also,  the  Galton  Laboratory  for  Eugenics,  founded  in  1905,  is  system- 
atically collecting  facts  about  human  pedigrees  and  publishing  the 
results  in  a  compendious  ''Treasury  of  Human  Inheritance." 

Besides  these  special  bureaus  of  investigation,  innumerable  facts 
about  the  inheritance  of  particular  traits  are  being  incidentally  brought 
together  and  made  available  in  various  institutions  and  asylums 
throughout  the  world  which  are  immediately  concerned  with  the  care 
of  defectives  of  different  types.  It  is  in  connection  with  such  institu- 
tions for  defectives  that  much  of  the  most  successful  ''field  work"  of 
the  Eugenics  Section  of  the  American  Breeders'  Association  is  being 
accomphshed  in  the  United  States. 

3.      FURTHER   APPLICATION   OF   WHAT   WE   KNOW   NECESSARY 

Human  performance  always  lags  behind  human  knowledge. 
Many  persons  who  are  fully  aware  of  the  right  procedure  do  not  put 
their  knowledge  into  practice.     It  follows,  therefore,  that  any  pro- 


HUMAN  COXSERVATION 


475 


gram  of  eugenics  which  does  not  grip  the  imagination  of  the  common 
people  in  such  a  way  as  to  become  an  effective  part  of  their  very  lives 
is  bound  to  remain  largely  an  academic  affair  for  Utopians  to  quarrel 
and  theorize  over. 

It  is  not  enough  to  collect  facts  and  work  out  an  analysis  and 
interpretation  of  them,  for,  important  as  this  preliminary  step  is,  it 
must  be  followed  by  a  convincing  campaign  of  education. 

The  lives  of  the  unborn  do  not  force  themselves  upon  the  average 
man  or  woman  with  the  same  insistency  as  the  lives  already  begun. 
In  the  midst  of  the  overwhelming  demands  of  the  present,  the  appeal 
of  posterity  for  better  blood  is  vague  and  remote.  If  every  individual 
regarded  the  germplasm  he  carries  as  a  sacred  trust,  then  it  would  be 
the  part  of  an  awakened  eugenic  conscience  to  restrain  that  germplasm 
when  it  is  known  to  be  defective  or,  when  it  is  not  defective,  to  hand 
it  on  to  posterity  with  at  least  as  much  foresight  as  is  exercised  in 
breeding  domestic  animals  and  cultivated  plants. 

The  eugenic  conscience  is  in  need  of  development,  and  it  is  only 
when  this  becomes  thoroughly  aroused  in  the  rank  and  file  of  society 
as  well  as  among,  the  leaders,  that  a  permanent  and  increasing  better- 
ment of  mankind  can  be  expected. 

4.      THE   RESTRICTION   OF   UNDESIRABLE   GERMPLASM 

A  negative  way  to  bring  about  better  blood  in  the  world  is  to 
follow  the  clarion  call  of  Davenport,  and  "dry  up  the  streams  that 
feed  the  torrent  of  defective  and  degenerate  protoplasm."  This  may 
be  partially  accomplished,  at  least  in  America,  by  employing  the 
following  agencies:  control  of  immigration;  more  discriminating 
marriage  laws;  a  quickened  eugenic  sentiment;  sexual  segregation  of 
defectives;  and  finally,  drastic  measures  of  asexualization  or  steriliza- 
tion when  necessary. 

a)       CONTROL   OF   IMMIGRATION 

The  enforcement  of  immigration  laws  tends  to  debar  from  the 
United  States  not  only  many  undesirable  individuals,  but  also  inci- 
dentally to  keep  out  much  potentially  bad  germplasm  that .  if  admitted, 
might  play  havoc  with  future  generations. 

For  example,  during  the  year  of  1908,  65  idiots,  121  feeble-minded, 
184  insane,  3,741  paupers,  2,900  individuals  having  contagious  dis- 
eases, 53  tuberculous  individuals,  136  criminals,  and  124  prostitutes 
were  caught  in  the  sieve  at  Ellis  Island  alone  and  turned  back  from 
this  country  by  the  immigration  officials.     These   7,000  and  more 


476      READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

individuals  probably  were  the  bearers  of  very  little  germplasm  that 
we  are  nationally  not  better  off  without. 

Eugenically,  the  weak  point  in  the  present  application  of  immi- 
gration laws  is  that  criteria  for  exclusion  are  phenotypic  in  nature 
rather  than  genotypic,  and  consequently  much  bad  germplasm  comes 
through  our  gates  hidden  from  the  view  of  inspectors  because  the 
bearers  are  heterozygous,  wearing  a  cloak  of  desirability  over  undesir- 
able traits. 

It  is  not  enough  to  lift  the  eyelid  of  a  prospective  parent  of  Ameri- 
can citizens  to  discover  whether  he  has  some  kind  of  an  eye-disease  or 
to  count  the  contents  of  his  purse  to  see  if  he  can  pay  his  own  way. 
The  official  ought  to  know  if  eye-disease  runs  in  the  immigrant's  family 
and  whether  he  comes  from  a  race  of  people  which,  through  chronic 
shiftlessness  or  lack  of  initiative,  have  always  carried  light  purses. 

In  selecting  horses  for  a  stock-farm  an  expert  horseman  might  rely 
to  a  considerable  extent  upon  his  judgment  of  horsbffesh  based  upon 
inspection  alone,  but  the  wise  breeder  does  more  than  take  the  chances 
of  an  ordinary  horse  trader.  He  wants  to  be  assur^  of  the  pedigree 
of  his  prospective  stock.  It  is  to  be  hoped  that  the  time  will  come 
when  we,  as  a  nation,  will  rise  above  the  hazardous  methods  of  the 
horse  trader  in  selecting  from  the  foreign  applicants  who  knock  at  our 
portals,  and  that  we  will  exercise  a  more  fundamental  discrimination 
than  such  a  haphazard  method  affords,  by  demanding  a  knowledge  of 
the  germplasm  of  these  candidates  for  citizenship,  as  displayed  in 
their  pedigrees. 

This  may  possibly  be  accomplished  by  having  trained  inspectors 
located  abroad  in  the  communities  from  which  our  immigrants  come, 
whose  duty  it  shall  be  to  look  up  the  ancestry  of  prospective  applicants 
and  to  stamp  desirable  ones  with  approval.  The  national  expense 
of  such  a  program  of  genealogical  inspection  would  be  far  less  than 
the  maintenance  of  introduced  defectives,  in  fact  it  would  greatly 
decrease  the  number  of  defectives  in  the  country.  At  the  present 
time  this  country  is  spending  over  one  hundred  million  dollars  a  year 
on  defectives  alone,  and  each  year  sees  this  amount  increased. 

The  United  States  Department  of  Agriculture  already  has  field 
agents  scouring  every  land  for  desirable  animals  and  plants  to  intro- 
duce into  this  country,  as  well  as  stringent  laws  to  prevent  the  importa- 
tion of  dangerous  weeds,  parasites,  and  organisms  of  various  kinds. 
Is  the  inspection  and  supervision  of  human  blood  less  important  ? 


HUMAN  COXSi:R\  ATIUX 


477 


b)      MORE   DISCRIMINATING    MARRIAGE    LAWS 

Every  people,  including  even  the  more  primitive  races,  make 
customs  or  laws  that  tend  to  regulate  marriage.  Of  these,  the  laws 
which  relate  to  the  eugenic  aspect  of  marriage  are  the  only  ones  that 
concern  us  in  this  connection.  ''Marriage,"  says  Davenport,  "can 
be  looked  at  from  many  points  of  view.  In  novels  as  the  climax  of 
human  courtship;  in  law  largely  as  two  lines  of  property  descent;  in 
society,  as  fixing  a  certain  status;  but  in  eugenics,  which  considers  its 
biological  aspect,  marriage  is  an  experiment  in  breeding." 

Certain  of  the  United  States  have  laws  forbidding  the  marriage 
of  epileptics,  the  insane,  habitual  drunkards,  paupers,  idiots,  feeble- 
minded, and  those  afflicted  with  venereal  diseases.  It  would  be  well 
if  such  laws  were  not  only  more  uniform  and  widespread,  but  also  more 
rigidly  enforced. 

It  is  quite  true  that  marriage  laws  in  themselves  do  not  necessarilv 
control  human  reproduction,  for  illegitimacy  is  a  factor  that  must 
always  be  reckoned  with;  nevertheless  such  laws  do  have  an  important 
influence  in  regulating  marriage  and  consequent  reproduction. 

Marriage  laws  may,  however,  sometimes  bring  about  a  deplor- 
able result  eugenically,  as  in  the  case  of  forced  marriage  of  sexual 
offenders  in  order  to  legalize  the  offense  and  ''save  the  woman's 
honor."  To  compel,  under  the  guise  of  legality,  two  defective  streams 
of  germplasm  to  combine  repeatedly  and  thereby  result  in  defective 
offspring  just  because  the  unfortunate  event  happened  once  illegiti- 
mately, is  fundamentally  a  mistake.  Darwin  says:  "E.xcept  in  the 
case  of  man  himself  hardly  any  one  is  so  ignorant  as  to  allow  his  worst 
animals  to  breed." 

c)      AN    EDUCATED    SENTIMENT 

A  far  more  effective  means  of  restricting  bad  germplasm  than 
placing  elaborate  marriage  laws  upon  our  statute-books  is  to  educate 
pubHc  sentiment  and  to  foster  a  popular  eugenic  conscience,  in  the 
absence  of  which  the  safeguards  of  the  law  must  forever  be  largely 
without  avail. 

Such  a  sentiment  already  generally  exists  to  a  large  extent  with 
respect  to  incest,  and  the  marriage  of  persons  as  noticeably  defective 
as  idiots  or  those  afflicted  with  insanity,  and  also  in  America  with 
respect  to  miscegenation,  but  a  cautious  and  intelligent  e.xamination 
of  the  more  obscure  defective  traits,  exhibited  in  the  somatoplasms  of 
the  various  members  of  families  in  question,  is  largely  an  ideal  of  the 


478      READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

future.  Under  existing  conditions  non-eugenic  considerations  such 
as  wealth,  social  position,  etc.,  often  enter  into  the  preliminary  negotia- 
tions of  a  marriage  alliance,  but  an  equally  unromantic  caution  with 
reference  to  the  physical,  moral,  and  mental  characters  that  make  up 
the  biological  heritage  of  contracting  parties  is  less  usual. 

The  scientific  attitude  is  not  necessarily  opposed  to  the  romantic 
way  of  looking  at  things.  Science  is  simple  ''organized  common 
sense,"  and  romance,  that  dispenses  with  this  balance-wheel,  although 
it  may  be  entertaining  and  always  exciting  at  first,  is  sure  to  be  dis- 
appointing in  the  end.  Marriages  may  be  "made  in  heaven,"  but, 
as  a  matter  of  fact,  children  are  born  and  have  to  be  brought  up  on 
earth.  It  follows  without  saying  that  it  will  be  much  easier  to  stamp 
out  bad  germplasm  when  an  educated  sentiment  becomes  common 
among  all  people  everywhere. 

d)      SEGREGATION    OF   DEFECTIVES 

Persons  with  hereditary  defects,  such  as  epileptics,  idiots,  and 
certain  criminals,  who  become  wards  of  the  state,  should  be  segregated 
so  that  their  germplasm  may  not  escape  to  furnish  additional  burdens 
to  society.  "We  have  become  so  used  to  crime,  disease  and  degener- 
acy that  we  take  them  for  necessary  evils.  That  they  were  in  the 
world's  ignorance,  is  granted.  That  they  must  remain  so,  is  denied" 
(Davenport). 

"The  great  horde  of  defectives  once  in  the  world  have  the  right  to 
live  and  enjoy  as  best  they  may  whatever  freedom  is  compatible  with 
the  lives  and  freedom  of  other  members  of  society,"  says  Kellicott,  but 
society  had  a  right  to  protect  itself  against  repetitions  of  hereditary 
blunders. 

There  is  one  grave  danger  connected  with  the  administration  of 
our  humane  and  commendable  philanthropies  toward  the  unfortunate, 
for  it  frequently  happens  that  defectives  are  kept  in  institutions  until 
they  are  sexually  mature  or  are  partly  self-supporting,  when  they  are 
liberated  only  to  add  to  the  burden  of  society  by  reproducing  their  like. 

Furthermore,  if  defectives  of  the  same  sort  are  collected  together 
in  the  same  institutions,  unless  sexual  segregation  is  strictly  main- 
tained, they  may  by  the  very  circumstance  of  proximity  tend  to 
reproduce  their  kind  just  as  defectives  in  any  isolated  community  tend 
to  multiply. 

David  Starr  Jordan  cites  the  interesting  case  of  cretinism  which 
occurs  in  the  valley  of  Aosta  in  northern  Italy,  to  prove  the  wisdom 


HUMAN'  COXSERVATIOX  479 

of  the  sexual  segregation  of  defectives.  Cretinism  is  an  hereditary 
defect  connected  with  an  abnormal  development  of  the  thyroid  gland 
which  results  in  a  peculiar  form  of  idiocy  usually  associated  with  goitre. 

*'In  the  city  of  Aosta  the  goitrous  cretin  has  been  for  centuries  an 
object  of  charity.  The  idiot  has  received  generous  support,  while  the 
poor  farmer  or  laborer  with  brains  and  no  goitre  has  had  the  severest 
of  struggles.  In  the  competition  of  life  a  premium  has  thus  been 
placed  on  imbecility  and  disease.  The  cretin  has  mated  with  cretin, 
the  goitre  with  goitre,  and  charity  and  religion  have  presided  over 
the  union.  The  result  is  that  idiocy  is  multiplied  and  intensified.  The 
cretin  of  Aosta  has  been  developed  as  a  new  species  of  man.  In  fair 
weather  the  roads  about  the  city  are  lined  with  these  awful  paupers — 
human  beings  with  less  intelligence  than  a  goose,  with  less  decency 
than  the  pig." 

Whymper,  writing  in  1880,  further  observes:  "It  is  strange  that 
self-interest  does  not  lead  the  natives  of  Aosta  to  place  their  cretins 
under  such  restrictions  as  would  prevent  their  illicit  intercourse;  and 
it  is  still  more  surprising  to  find  the  Catholic  Church  actually  legalizing 
their  marriage.  There  is  something  horribly  grotesque  in  the  idea  of 
solemnizing  the  union  of  a  brace  of  idiots,  and,  since  it  is  well  known 
that  the  disease  is  hereditary  and  develops  in  successive  generations  the 
fact  that  such  marriages  are  sanctioned  is  scandalous  and  infamous.'' 

Since  1890  the  cretins  have  been  sexually  segregated,  and  in  1910 
Jordan  reported  that  they  were  nearly  all  gone. 

e)      DRASTIC   MEASURES 

A  fifth  method  of  restricting  undesirable  germplasm  in  the  case  of 
confirmed  criminals,  idiots,  imbeciles,  and  rapists  may  be  mentioned, 
namely,  the  extreme  treatment  of  either  asexualization  or  vasectomy. 
The  latter  is  a  minor  operation  confined  to  the  male  which  occupies 
only  a  few  moments  and  requires  at  most  only  the  application  of  a 
local  anaesthetic,  such  as  cocaine.  There  are  no  disturbing  or  even 
inconvenient  after  effects  from  this  operation.  It  consists  in  removing 
a  small  section  of  each  sperm  duct,  and  is  entirely  effectual  in  prevent- 
ing subsequent  parenthood. 

In  the  female  the  corresponding  operation,  which  consists  in 
removing  a  portion  of  each  Fallopian  tube,  is  much  more  severe,  but 
not  impracticable  or  dangerous. 

Eight  states  already  have  sterilization  laws  providing  lor  certain 
(^ses  and  ''could  such  a  law  be  enforced  in  the  whole  United  States, 


480      READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

less  than  four  generations  would  eliminate  nine  tenths  of  the  crime, 
insanity  and  sickness  of  the  present  generation  in  our  land.  Asylums, 
prisons  and  hospitals  would  decrease,  and  the  problems  of  the  unem- 
ployed, the  indigent  old  and  the  hopelessly  degenerate  would  cease  to 
trouble  civilization." 

5.      THE   CONSERVATION   OF   DESIRABLE    GERMPLASM 

Not  only  negatively  by  the  restriction  of  undesirable  germplasm, 
but  also  positively  by  the  conservation  of  desirable  germplasm,  may 
the  eugenic  ideal  be  approached. 

It  is  possible  that  if  some  of  the  philanthropic  endeavor  now 
directed  toward  alleviating  the  condition  of  the  unfit  should  be  directed 
to  enlarging  the  opportunity  of  the  fit,  greater  good  would  result  in  the 
end.  In  breeding  animals  and  plants  the  most  notable  advances  have 
been  made  by  isolating  and  developing  the  best,  rather  than  by 
attempting  to  raise  the  standard  of  mediocrity  through  the  elimination 
of  the  worst. 

One  leader  is  worth  a  score  of  followers  in  any  community,  and  the 
science  of  genetics  surely  gives  to  educators  the  hint  that  it  is  wiser 
to  cultivate  the  exceptional  pupil  who  is  often  left  to  take  care  of  him- 
self than  to  expend  all  the  energies  of  the  instructor  in  forcing  the 
indifferent  or  ordinary  one  up  to  a  passing  standard.  The  campaign 
for  human  betterment  in  the  long  run  must  do  more  than  avoid  mis- 
takes. It  must  become  aggressive  and  take  advantage  of  those  human 
mutations  or  combinations  of  traits  which  appear  in  the  exceptionally 
endowed. 

There  are  various  ways  in  which  this. improvement  of  society  may 
be  brought  about. 

a)      BY   SUBSIDIZING   THE   FIT 

The  following  unconfirmed  newspaper  clipping  illustrates  the 
point  of  what  is  meant  by  subsidizing  the  fit  so  far  as  certain  physical 
characteristics  are  concerned.  "Berlin,  Dec.  11,  1911.  The  Emperor 
is  reported  to  be  interested  in  a  plan  proposed  by  Professor  Otto 
Hauser  for  the  propagation  of  a  fixed  German  type  of  humanity — 
a  type  which  will  be  as  fixed  as  the  Jewish  in  its  characteristics,  if  the 
suggestions  of  the  professor  can  ever  be  carried  out.  The  fixed  type 
is  to  be  produced  as  follows : — Only  '  typical '  couples  are  to  be  allowed 
to  mate.  The  man  is  to  be  not  more  than  thirty  years  old,  the  woman 
not  over  twenty-eight,  and  each  have  a  perfect  health  certificate.  The 
man  should  be  at  least  five  feet  seven  inches  tall;  the  woman  not  undear 


HUMAN  COXSERVATIOX  481 

five  feet  six  inches.  Neither  the  man  nor  the  woman  should  have  dark 
hair.  Its  tint  may  range  from  blonde  to  auburn.  'I'he  eyes  of  the 
pair  should  be  pure  blue  without  any  tint  of  brown.  The  complexion 
should  be  fair  to  ruddy  without  any  suggestion  of  heaviness  or  '  beefi- 
ness.'  The  nose  ought  to  be  strong  and  narrow,  the  chin  square  and 
powerful,  and  the  skull  well  developed  at  the  back.  The  man  and  the 
woman  must  be  of  German  descent  and  must  bear  a  German  name  and 
speak  the  language  of  Germany.  These  'mated  couples'  are  to  get 
a  wedding  gift  of  $125  and  an  additional  grant  for  each  child  born. 
The  couples  may  settle  in  the  United  States  if  they  prefer."  This 
reported  attempt  to  establish  a  Prussian  iyn[)e  of  ''Hauser  blondes''  at 
least  points  the  way  to  one  sort  of  a  positive  eugenic  method  that 
might  possibly  be  employed  with  respect  to  certain  physical  charac- 
teristics. 

It  should  be  remembered,  however,  that  the  eugenic  ideal  is  not 
by  any  means  confined  to  physical  traits  alone. 

b)      BY   ENLARGING   INDR^IDUAL   OPPORTUNITY 

Much  good  human  germplasm  goes  to  waste  through  inetTective- 
ness  on  account  of  unfavorable  environment  or  lack  of  a  suitable 
opportunity  to  develop. 

Every  agency  which  contributes  toward  increasing  the  opportunity 
of  the  individual  to  attain  to  a  better  development  of  his  latent 
possibilities  is  in  harmony  wdth  a  thoroughly  positive  eugenic  practice. 
Thus  better  schools,  better  homes,  better  living  conditions,  in  short, 
all  euthenic  endeavor,  directly  serves  the  eugenic  ideal  by  making  the 
best  out  of  whatever  germinal  equipment  is  present  in  man. 

C)      BY   PREVENTING   GERMINAL    WASTE 

Much  good  protoplasm  fails  to  find  expression  in  the  form  of  off- 
spring because  one  or  the  other  of  possible  parents  is  cut  off  either  by 
preventable  death  or  by  social  hindrances.  To  avoid  such  calamities 
is  a  part  of  the  positive  program  of  eugenics. 

I.  Preventable  death. — War,  from  the  eugenic  point  of  view,  is  the 
height  of  folly,  since  presumably  the  brave  and  the  physically  fit 
march  away  to  fight,  while  in  general  the  unqualified  stay  at  home  to 
reproduce  the  next  generation.  When  a  soldier  dies  on  the  battlefield 
or  in  the  hospital,  it  is  not  alone  a  brave  man  who  is  cut  off,  but  it  is 
the  termination  of  a  probably  desirable  strain  of  germplasm.  The 
Thirty  Years'  War  in  Germany  cost  6,000,000  lives,  while  Naix)leon 
in  his  campaigns  drained  the  best  blood  of  France. 


482      READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

David  Starr  Jordan  has  presented  the  matter  very  clearly.  He 
points  out  that  the  ''man  with  a  hoe"  among  the  European  peasantry 
is  not  the  result  of  centuries  of  oppression,  as  he  has  been  pictured,  but 
rather  the  dull  progeny  resulting  from  generations  of  the  unfit  who 
were  left  behind  when  the  fit  went  off  to  war  never  to  return. 

Benjamin  Franklin,  with  characteristic  wisdom,  sums  up  the 
situation  in  the  following  epigram:  "Wars  are  not  paid  for  in  war 
time;   the  bill  comes  later." 

2.  Social  Hindrances. — There  are  many  conditions  of  modern 
society  which  act  non-eugenically. 

For  instance,  the  increasing  demands  of  professional  life  prolong 
the  period  necessary  for  preparation,  which,  with  the  ''cost  of  high 
living,"  tends  toward  late  marriage.  In  this  way  much  of  the  best 
germplasm  is  very  often  withheld  from  circulation  until  it  is  too  late 
to  be  effective  in  providing  for  the  succeeding  generation. 

Certain  occupations  such  as  school-teaching  and  nursing  by 
women  are  filled  by  the  best  blood  obtainable,  yet  this  blood  is  denied 
a  direct  part  in  molding  posterity,  since  marriage  is  either  forbidden  or 
regarded  as  a  serious  handicap  in  such  lines  of  work.  Advertisements 
concerning  "unincumbered  help"  and  "childless  apartments"  tell 
their  own  deplorable  tale. 

One  of  the  darkest  features  of  the  dark  ages  from  a  eugenic  stand- 
point was  the  enforced  celibacy  of  the  priesthood,  since  this  resulted, 
as  a  rule,  in  withdrawing  into  monasteries  and  nunneries  much  of  the 
best  blood  of  the  times,  and  this  uneugenic  custom  still  obtains  in 
many  quarters  today. 

6.      \VH.O   SHALL   SIT   IN   JUDGMENT? 

In  the  practical  application  of  a  program  of  eugenics  there  are 
many  difficulties,  for  who  is  qualified  to  sit  in  judgment  and  separate 
the  fit  from  the  unfit  ? 

There  are  certain  strongly  marked  characteristics  in  mankind 
which  are  plainly  good  or  bad,  but  the  principle  of  the  independence 
of  unit  characters  demonstrates  that  no  person  is  wholly  good  or 
wholly  bad.  Shall  we  then  throw  away  the  whole  bundle  of  sticks 
because  it  contains  a  few  poor  or  crooked  ones  ? 

The  list  of  weakhng  babies,  for  instance,  who  were  apparently 
physically  unfit  and  hardly  worth  raising  upon  first  judgment,  but  who 
afterwards  became  powerful  factors  in  the  world's  progress,  is  a  notable 
one  and  includes  the  names  of  Calvin,  Newton,  Heine,  Voltaire, 
Herbert  Spencer,  and  Robert  Louis  Stevenson. 


HUMAN  CONSERVATION  483 

Or,  take  another  example.  Elizal^cth  Tuttle,  the  grandmother  of 
Jonathan  Edwards  whose  remarkable  progeny  was  referred  to  in  a 
preceding  chapter,  is  described  as  a  "woman  of  great  beauty,  of  tall 
and  commanding  appearance,  striking  carriage,  of  strong  will,  extreme 
intellectual  vigor  and  mental  grasp  akin  to  rapacity,"  but  with  an 
extraordinary  deficiency  in  moral  sense.     She  was  divorced  from  her 

husband  "on  the  ground  of  adultery  and  other  immoralities 

The  evil  trait  was  in  the  blood,  for  one  of  her  sisters  murdered  her 
own  son  and  a  brother  murdered  his  own  sister."  That  Jonathan 
Edwards  owed  his  remarkable  qualities  largely  to  his  grandmother 
rather  than  to  his  grandfather  is  shown  by  the  fact  that  Richard 
Edwards,  the  grandfather,  married  again  after  his  divorce  and  had 
five  sons  and  one  daughter,  but  none  of  their  numerous  progeny  "  rose 
above  mediocrity,  and  their  descendants  gained  no  abiding  reputa- 
tion." As  shown  by  subsequent  events,  it  would  have  been  a  great 
eugenic  mistake  to  have  deprived  the  world  of  Elizabeth  Tuttle's 
germp^asm,  although  it  would  have  been  easy  to  find  judges  to  con- 
demn her. 

Dr.  C.  V.  Chapin  recently  said  with  reference  to  the  eugenic 
regulation  of  marriage  by  physician's  certificate:  "The  causes  of 
heredity  are  many  and  very  conflicting.  The  subject  is  a  difficult  one, 
and  I  for  one  would  hesitate  to  say,  in  a  great  many  cases  where  I  have 
a  pretty  good  knowledge  of  the  family,  where  marriage  would,  or 
would  not,  be  desirable." 

Desirability  and  undesirability  must  always  be  regarded  as  rela- 
tive terms  more  or  less  indefinable.  In  attempting  to  define  them,  it 
makes  a  great  difference  whether  the  interested  party  holds  to  a 
puritan  or  a  cavalier  standard.  To  show  how  far  human  judgment 
may  err  as  well  as  how  radically  human  opinion  changes,  there  were  in 
England,  as  recently  as  1819,  233  crimes  punishable  by  death  accord- 
ing to  law. 

One  needs  only  to  recall  the  days  of  the  Spanish  Inquisition  or  of 
the  Salem  witchcraft  persecution  to  realize  what  fearful  blunders 
human  judgment  is  capable  of,  but  it  is  unlikely  that  the  world  will 
ever  see  another  great  religious  inquisition,  or  that  in  applying  to  man 
the  newly  found  laws  of  heredity  there  will  ever  be  undertaken  an 
equally  deplorable  eugenic  inquisition. 

It  is  quite  apparent,  finally,  that  although  great  caution  and 
broadness  of  vision  must  be  exercised  in  bringing  about  the  fulfilment 
of  the  highest  eugenic  ideals,  nevertheless  in  this  direction  lies  the 
future  path  of  human  achievement. 


CHAPTER  XXXVI 
EUGENICS  AND  EUTHENICS^ 

PAUL  POPENOE  AND  ROSWELL  H.  JOHNSON 

I 

Emphasis  has  been  given,  in  several  of  the  foregoing  chapters,  to 
the  desirabihty  of  inheriting  a  good  constitution  and  a  high  degree 
of  vigor  and  disease-resistance.  It  has  been  asserted  that  no  measures 
of  hygiene  and  sanitation  can  take  the  place  of  such  inheritance.  It 
is  now  desirable  to  ascertain  the  limits  within  which  good  inheritance 
is  effective,  and  this  may  be  conveniently  done  by  a  study  of  the  lives 
of  a  group  of  people  who  inherited  exceptionally  strong  physical  con- 
stitutions. 

The  people  referred  to  are  taken  from  a  collection  of  histories  of 
long  life  made  by  the  Genealogical  Record  Office  of  Washington. 
One' hundred  individuals  were  picked  out  at  random,  each  of  whom  had 
died  at  the  age  of  ninety  or  more,  and  with  the  record  of  each  indi- 
vidual were  placed  those  of  all  his  brothers  and  sisters.  Any  family 
was  rejected  in  which  there  was  a  record  of  wholly  accidental  death 
(e.g.,  families  of  which  a  member  had  been  killed  in  the  Civil  War). 
The  loo  families,  or  more  correctly  fraternities  or  sibships,  were 
classified  by  the  number  of  children  per  fraternity,  as  follows : 


Number 

of 
raternities 

Number  of 

Children  per 

Fraternity 

Total  Number 

of  Children 

in  Group 

I 

2 

2 

II 

3 

33 

8 

4 

32 

17 

5 

85 

13 

6 

78 

14 

7 

98 

9 

8 

72 

II 

9 

99 

10 

10 

100 

3 

II 

33 

2 

12 

24 

V         I 

13 

13 

TOO  669 

I  From  P.  Popenoe  and  R.  H.  Johnson,  Applied  Eugenics  (copyright  1918). 
Used  by  special  permission  of  the  publishers,  The  Macmillan  Company. 

484 


EUGENICS  AND  EUTHENICS  485 

The  average  at  death  of  these  669  persons  was  64.7  years.  The 
child  mortahty  (first  4  years  of  Ufe)  was  7.5  per  cent  of  the  total 
mortality,  69  families  showing  no  deaths  of  that  kind.  The  group 
is  as  a  whole,  therefore,  long-lived. 

The  problem  was  to  measure  the  resemblance  between  brothers  and 
sisters  in  respect  of  longevity — to  find  whether  knowledge  of  the  age 
at  which  one  died  would  justify  a  prediction  as  to  the  age  at  death  of 
the  others — or  technically,  it  was  to  measure  the  fraternal  correlation 
of  longevity.  A  zero  coefficient  here  would  show  that  there  is  no 
association;  that  from  the  age  at  which  one  dies,  nothing  whatever 
can  be  predicted  as  to  the  age  at  which  the  others  will  die.  Since  it  is 
known  that  heredity  is  a  large  factor  in  longevity,  such  a  finding  would 
mean  that  all  deaths  were  due  to  some  accident  which  made  the 
inheritance  of  no  account. 

In  an  ordinary  population  it  has  been  found  that  the  age  at  death 
of  brothers  and  sisters  furnishes  a  coefticient  of  correlation  of  the  order 
of  .3,  which  shows  that  heredity  does  determine  the  age  at  which  one 
shall  die  to  considerable  extent,  but  not  absolutely.^ 

The  index  of  correlation^  between  the  lengths  of  life  within  the 
fraternity  in  these  100  selected  families,  furnished  a  coefficient  of 
—  .0163  ±  .0672,  practically  zero.  In  other  words,  if  the  age  is  known 
at  which  a  member  of  one  of  these  families  died,  whether  it  be  one 
month  or  100  years,  nothing  whatever  can  be  predicted  about  the  age 
at  which  his  brothers  and  sisters  died. 

'  Mary  Beeton,  and  Karl  Pearson,  Biometrika,  I,  p.  60.  The  actual  correlation 
varies  with  the  age  and  sex:   the  following  are  the  results: 

COLLATERAL   INHERITANCE 

Elder  adult  brother  and  younger  adult  brother 2290^  0194 

Adult  brother  and  adult  brother 2853=*=  .0196 

Minor  brother  and  minor  brother 1026=*=  .0294 

Adult  brother  and  minor  brother —  .0262^  .0246 

Elder  adult  sister  and  younger  adult  sister 3464=*=  .0183 

Adult  sister  and  adult  sister 3322±  .0185 

Minor  sister  and  minor  sister 1748='=  .0307 

Adult  sister  and  minor  sister —  .0260=^  .0291 

Adult  brother  and  adult  sister 2319=*=  .0145 

Minor  brother  and  minor  sister i43S=*=  0251 

Adult  brother  and  minor  sister —  .oo02±  .0349 

Adult  sister  and  minor  brother —  .0274=*=  .0238 

2  The  method  used  is  the  ingenious  one  devised  by  J.  Arthur  Harris 
(Biometrika,  IX,  p.  461).     The  probable  error  is  based  on  ?i=  100. 


486      READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

Remembering  that  longevity  is  in  general  inherited,  and  that  it  is 
found  in  the  families  of  all  the  people  of  this  study  (since  one  in  each 
fraternity  lived  to  be  90  or  over)  how  is  one  to  interpret  this  zero 
coefficient?  Evidently  it  means  that  although  these  people  had 
inherited  a  high  degree  of  longevity,  their  deaths  were  brought  about 
by  causes  which  prevented  the  heredity  from  getting  full  expression. 
As  far  as  hereditary  potentialities  are  concerned,  it  can  be  said  that  all 
their  deaths  were  due  to  accident,  using  that  word  in  a  broad  sense  to 
include  all  non-selective  deaths  by  disease.  If  they  had  all  been  able 
to  get  the  full  benefit  of  their  heredity,  it  would  appear  that  each  of 
these  persons  might  have  lived  to  90  or  more,  as  did  the  one  in  each 
family  who  was  recorded  by  the  Genealogical  Record  Office.  Geneti- 
cally, these  other  deaths  may  be  spoken  of  as  premature. 

In  an  ordinary  population,  the  age  of  death  is  determined  to  the 
extent  of  probably  50  per  cent  by  heredity.  In  this  selected  long- 
lived  population,  heredity  appears  not  to  be  responsible  in  any  meas- 
urable degree  whatsoever  for  the  differences  in  age  at  death. 

The  result  may  be  expressed  in  another,  and  perhaps  more  striking, 
way.  Of  the  669  individuals  studied,  a  hundred — namely,  one  child 
in  each  family — lived  beyond  90;  and  there  were  a  few  others  who  did. 
But  some  550  of  the  group,  though  they  had  inherited  the  potentiality 
of  reaching  the  average  age  of  90,  actually  died  somewhere  around  60; 
they  failed  by  at  least  one-third  to  live  up  to  the  promise  of  their 
inheritance.  If  we  were  to  generalize  from  this  single  case,  we  would 
have  to  say  that  five-sixths  of  the  population  does  not  make  the  most 
of  its  physical  inheritance. 

This  is  certainly  a  fact  that  discourages  fatalistic  optimism.  The 
man  who  tells  himself  that,  because  of  his  magnificent  inherited 
constitution,  he  can  safely  take  any  risk,  is  pretty  sure  to  take  too 
many  risks  and  meet  with  a  non-selective — i.e.,  genetically,  a  pre- 
mature— death,  when  he  might  in  the  nature  of  things  have  lived 
almost  a  generation  longer. 

It  should  be  remarked  that  most  of  the  members  of  this  group 
seem  to  have  lived  in  a  hard  environment.  They  appear  to  belong 
predominantly  to  the  lower  strata  of  society;  many  of  them  are  immi- 
grants and  only  a  very  few  of  them,  to  judge  by  a  cursory  inspection 
of  the  records,  possessed  more  than  moderate  means.  This  necessi- 
tated a  frugal  and  industrious  life  which  in  many  ways  was  favorable 
to  longevity  but  which  may  often  have  led  to  overexposure,  overwork, 
lack  of  proper  medical  treatment,  or  other  causes  of  a  non-selective 


EUGENICS  AND  EUTHEMCS  487 

death.  We  would  not  push  the  conclusion  too  far,  but  we  can  not 
doubt  that  this  investigation  shows  the  folly  of  ignoring  the  environ- 
ment— shows  that  the  best  inherited  constitution  must  have  a  fair 
chance.  And  what  has  here  been  found  for  a  physical  character, 
would  probably  hold  good  in  even  greater  degree  for  a  mental  charac- 
ter. All  that  man  inherits  is  the  capacity  to  develop  along  a  certain 
line  under  the  influence  of  proper  stimuli,  food  and  exercise.  The 
object  of  eugenics  is  to  see  that  the  inherent  capacity  is  there.  Given 
that,  the  educational  system  is  next  needed  to  furnish  the  stimuli. 
The  consistent  eugenist  is  therefore  an  ardent  euthenist.  He  not  only 
works  for  a  better  human  stock  but,  because  he  does  not  want  to  see 
his  efforts  wasted,  he  always  works  to  provide  the  best  possible  envi- 
ronment for  this  better  stock. 

In  so  far,  then,  as  euthenics  is  actually  providing  man  with  more 
favorable  surroundings — not  with  ostensibly  more  favorable  sur- 
roundings which,  in  reality,  are  unfavorable — there  can  be  no  antago- 
nism between  it  and  eugenics.  Eugenics  is,  in  fact,  a  prerequisite  of 
euthenics,  for  it  is  only  the  capable  and  altruistic  man  who  can  con- 
tribute  to  social  progress;  and  such  a  man  can  only  be  produced 
through  eugenics. 

Eugenic  fatalism,  a  blind  faith  in  the  omnipotence  of  heredity 
regardless  of  the  surroundings  in  which  it  is  placed,  has  been  shown 
by  the  study  of  long-lived  families  to  be  unjustified.  It  was  found 
that  even  those  who  inherited  exceptional  longevity  usually  did  not 
live  as  long  as  their  inheritance  gave  them  the  right  to  expect.  If  they 
had  had  more  euthenics,  they  should  have  lived  longer. 

But  this  illustration  certainly  gives  no  ground  for  a  belief  that 
euthenics  is  sufficient  to  prolong  one's  life  beyond  the  inherited  limit. 
A  study  of  these  long-lived  families  from  another  point  of  view  will 
reveal  that  heredity  is  the  primary  factor  and  that  good  environment, 
euthenics,  is  the  secondary  one. 

For  this  purpose  we  augment  the  100  families  of  the  preceding 
section  by  the  addition  of  240  more  families  like  them,  and  we  examine 
each  family  history  to  find  how  many  of  the  children  died  before  com- 
pleting the  fourth  year  of  Hfe.  The  data  are  summarized  in  the  tal)le 
on  page  488. 

The  addition  of  the  new  families  (which  were  not  subjected  to  any 
different  selection  than  the  first  100)  has  brought  down  the  child 
mortality  rate.  For  the  first  100,  it  was  found  to  be  7.5  per  cent.  If 
in  the  above  table  the  number  of  child  deaths,  119,  be  divided  by  the 


488      READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

total  number  of  children  represented,  2,259,  the  child  mortality  rate 
for  this  population  is  found  to  be  5.27  per  cent  or  53  per  1,000. 

The  smallness  of  this  figure  may  be  seen  by  comparison  with  the 
statistics  of  the  registration  area,  U.S.  Census  of  1880,  when  the  child 
mortality  (0-4  years)  was  400  per  thousand,  as  calculated  by  Alexan- 
der Graham  Bell.  A  mortality  of  53  for  the  first  four  years  of  life  is 
smaller  than  any  district  known  in  the  United  States,  even  to-day,  can 
show  for  the  first  year  of  life  alone.  If  any  city  could  bring  the  deaths 
of  babies  during  their  first  twelve  months  down  to  53  per  1,000,  it 
would  think  it  had  achieved  the  impossible;  but  here  is  a  population 

CHILD  MORTALITY  IN  FAMILIES  OF  LONG-LIVED  STOCK, 
GENEALOGICAL  RECORD  OFFICE  DATA 


Size 
of 
"amily 

Number  of 

Families 
Investigated 

Number  of  Families 
Showing  Deaths 
under  Five  Years 

Total  Nun 
of 
Deaths 

I  child 

6 

0 

0 

2  children 

6 

0 

0 

3 

38 

4 

s 

4 

40 

6 

7 

5 

38 

4 

4 

6 

44 

12 

13 

7 

34 

8 

II 

8 

46 

13 

18 

9 

31 

14 

20 

10 

27 

14 

14 

II 

13 

6 

9 

12 

13 

9 

16 

13 

I 

0 

0 

14 

2 

0 

0 

17 

I 

I 

2 

340  91  119 

in  which  53  per  1,000  covers  the  deaths,  not  only  of  the  fatal  first  12 
months,  but  of  the  following  three  years  in  addition. 

Now  this  population  with  an  unprecedentedly  low  rate  of  child 
mortality  is  not  one  which  had  had  the  benefit  of  any  Baby  Saving 
Campaign,  nor  even  the  knowledge  of  modern  science.  Its  mothers 
were  mostly  poor,  many  of  them  ignorant;  they  lived  frequently 
under  conditions  of  hardship ;  they  were  peasants  and  pioneers.  Their 
babies  grew  up  without  doctors,  without  pasteurized  milk,  without  ice, 
without  many  sanitary  precautions,  usually  on  rough  food.  But  they 
had  one  advantage  which  no  amount  of  applied  science  can  give  after 
birth — namely,  good  heredity.  They  had  inherited  exceptionally 
good  constitutions. 


EUGENICS  AND  EUTHENICS 


489 


It  is  not  by  accident  that  inherited  lonp;evily  in  a  family  is  associ- 
ated with  low  mortality  of  its  children.  The  connection  between  the 
two  facts  was  first  discovered  by  Alary  Beeton  and  Karl  Pearson  in 
their  pioneer  work  on  the  inheritance  of  duration  of  life.  They  found 
that  high  infant  mortality  was  associated  with  early  death  of  parents, 
while  the  offspring  of  long-lived  parents  showed  few  deaths  in  child- 
hood. The  correlation  of  the  two  facts  was  quite  regular,  as  will  be 
evident  from  a  glance  at  the  following  tables  prepared  by  A.  Ploetz: 

LENGTH  OF  LIFE  OF  MOTHERS  AND  CHILI)  MORTALITY  OF  THEIR 

DAUGHTERS    (ENGLISH    QUAKER    F.VMILIES,    DATA    OF 

BEETON  AND  PEARSON,  ARRANGED  HV  PLOETZ) 


All 
/\ges 

1,846 

511 
27.7 


Number  of  daughters 

Number  of  them  who  died  in  first  five 

years 

Per  cent  of  daughters  who  died 


Year  of  Life  in  Which 

Mothers  Died 

to  38 

39-53 

54-68 

69-83 

84  up 

234 

304 

395 

666 

247 

122 

114 

118 

131 

26 

52.1 

37-5 

29.9 

19.7 

10.5 

LENGTH  OF  LIFE  OF  FATHERS  AND  CHILD  IMORTALITV  OF 

THEIR  DAUGHTERS 


Number  of  daughters 

Number  of  them  who  died  in  first  five 

years 

Per  cent  of  daughters  who  died. . . 


Year  of  Life  in  Which 

Fathers  Died 

to  38 

39-53 

54-68 

69-83 

84  up 

105 

51 
48.6 

284 

98 
34-5 

585 

156 
26.7 

797 

177 
22.2 

236 

40 
17.0 

At 
All 

Ages 


2,009 

522 
26.0 


To  save  space,  we  do  not  show  the  relation  between  parent  and 
son;  it  is  similar  to  that  of  parent  and  daughter  which  is  shown  in  the 
preceding  tables.  In  making  comparison  with  the  340  families  from 
the  Genealogical  Record  Office,  above  studied,  it  must  be  noted  that 
Dr.  Ploetz's  tables  include  one. year  longer  in  the  period  of  child  mor- 
tality, being  computed  for  the  first  five  years  of  life  instead  of  the  first 
four.  His  percentages  would  therefore  be  somewhat  lower  if  com- 
puted on  the  basis  used  in  the  American  work. 

These  various  data  demonstrate  the  existence  of  a  considerable 
correlation  between  short  life  {bracJiybioty,  Karl  Pearson  calls  it)  in 
parent  and  short  life  in  offspring.  Not  only  is  the  tendency  to  live 
long  inherited,  but  the  tendency  not  to  live  long  is  likewise  inherited. 


490      READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

But  perhaps  the  reader  may  think  they  show  nothing  of  the  sort. 
He  may  fancy  that  the  early  death  of  a  parent  left  the  child  without 
sufficient  care,  and  that  neglect,  poverty,  or  some  other  factor  of 
euthenics  brought  about  the  child's  death.  Perhaps  it  lacked  a 
mother's  loving  attention,  or  perhaps  the  father's  death  removed  the 
wage-earner  of  the  family  and  the  child  thenceforth  lacked  the 
necessities  of  life. 

Dr.  Ploetz  has  pointed  out  that  this  objection  is  not  valid,  because 
the  influence  of  the  parent's  death  is  seen  to  hold  good  even  to  the 
point  where  the  child  was  too  old  to  require  any  assistance.  If  the 
facts  applied  only  to  cases  of  early  death,  the  supposed  objection 
might  be  weighty,  but  the  correlation  exists  from  one  end  of  the  age- 
scale  to  the  other.  It  is  not  credible  that  a  child  is  going  to  be  deprived 
of  any  necessary  maternal  care  when  its  mother  dies  at  the  age  of  69 ; 
the  child  herself  was  probably  married  long  before  the  death  of  the 
mother.  Nor  is  it  credible  that  the  death  of  the  father  takes  bread 
from  the  child's  mouth,  leaving  it  to  starve  to  death  in  the  absence  of  a 
pension  for  widowed  mothers,  if  the  father  died  at  83,  when  the  ^'  child  " 
herself  was  getting  to  be  an  old  woman.  The  early  death  of  a  parent 
may  occasionally  bring  about  the  child's  death  for  a  reason  wholly 
unconnected  with  heredity,  but  the  facts  just  pointed  out  show  that 
such  cases  are  exceptional.  The  steady  association  of  the  child  death- 
rate  and  parent  death-rate  at  all  ages  demonstrates  that  heredity  is  a 
common  cause. 

But  the  reader  may  suspect  another  fallacy.  The  cause  of  this 
association  is  really  environmental,  he  may  think,  and  the  same 
poverty  or  squalor  which  causes  the  child  to  die  early  may  cause  the 
parent  to  die  early.  They  may  both  be  of  healthy,  long-lived  stock, 
but  forced  to  live  in  a  pestiferous  slum  which  cuts  both  of  them 
off  prematurely  and  thereby  creates  a  spurious  correlation  in  the 
statistics. 

We  can  dispose  of  this  objection  most  effectively  by  bringing  in 
new  evidence.  It  will  probably  be  admitted  that  in  the  royal  families 
of  Europe,  the  environment  is  as  good  as  knowledge  and  wealth  can 
make  it.  No  child  dies  for  lack  of  plenty  of  food  and  the  best  medical 
care,  even  if  his  father  or  mother  died  young.  And  the  members  of 
this  caste  are  not  exposed  to  any  such  unsanitary  conditions,  or  such 
economic  pressure  as  could  possibly  cause  both  parent  and  child  to  die 
prematurely.  If  the  association  between  longevity  of  parent  and 
child  mortality  holds  for  the  royal  families  of  Europe  and  their  princely 


EUGENICS  AXD  EUTHEXICS 


491 


relatives,  it  can  hardly  be  regarded  as  anything  but  the  effect  of 
heredity — of  the  inheritance  of  a  certain  type  of  constitution. 

Dr.  Ploetz  studied  the  deaths  of  3, 2 10  children  in  European  royalty, 
from  this  viewpoint.  The  following  table  shows  the  relation  between 
father  and  child : 

LENGTH  OF  LIFE  OF  FATPIERS  AND  CHILD  MORTALITY'  OF 
THEIR  CHILDREN  IN  ROYAL  AND  PRLXCELY 
FAMILIES  (PLOETZ  DATA) 


Year  of  Life  in  Which  Fathers  Died 

At 

All 

Ages 

16-25 

23 
12 

52.2 

26-35 

36-45 

46-55 

56-65 

66-75 

1 
76-85  86  up 

Number  of  children 

90 

29 

32.2 

367 

115 

31-3 

545 
171 

31-4 

725 
200 
27.6 

983 

254 

25.8 

444 

105 
23.6 

33 
I 

3c 

3210 
887 
27.6 

Number  who  died  in  first  five  years. 
Per  cent  who  died 

Allowing  for  the  smallness  of  some  of  the  groups,  it  is  evident  that  the 
amount  of  correlation  is  about  the  same  here  as  among  the  English 
Quakers  of  the  Beeton-Pearson  investigation,  whose  mortality  was 
shown  in  the  two  preceding  tables.  In  the  healthiest  group  from  the 
royal  families — the  cases  in  which  the  father  lived  to  old  age — the 
amount  of  child  mortality  is  about  the  same  as  that  of  the  Hyde  family 
in  America,  which  Alexander  Graham  Bell  has  studied — namely, 
somewhere  around  250  per  1,000.  One  may  infer  that  the  royal 
families  are  rather  below  par  in  soundness  of  constitution. 

All  these  studies  agree  perfectly  in  showing  that  the  amount  of 
child  mortahty  is  determined  primarily  by  the  physical  constitution 
of  the  parents,  as  measured  by  their  longevity.  In  the  light  of  these 
facts,  the  nature  of  the  extraordinarily  low  child  mortality  shown  in 
the  340  families  from  the  Genealogical  Record  Office,  with  which  we 
began  the  study  of  this  point,  can  hardly  be  misunderstood.  These 
families  have  the  best  inherited  constitution  possible  and  the  other 
studies  cited  would  make  us  certain  of  finding  a  low  child  mortality 
among  them,  even  if  we  had  not  directly  investigated  the  facts. 

If  the  interpretation  which  we  have  given  is  correct,  the  conclusion 
is  inevitable  that  child  mortality  is  primarily  a  problem  of  eugenics, 
and  that  all  other  factors  are  secondary.  There  is  found  to  be  no 
warrant  for  the  statement  so  often  repeated  in  one  form  or  another, 
that  "  the  fundamental  cause  of  the  excessive  rate  of  infant  mortality 
in  industrial  communities  is  poverty,  inadequate  incomes,  and  low 
standards  of  living."     Royalty  and  its  princely  relatives  arc  not 


492      READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

characterized  by  a  low  standard  of  living,  and  yet  the  child  mortality 
among  them  is  very  high — somewhere  around  400  per  1,000  in  cases 
where  a  parent  died  young.  If  poverty  is  responsible  in  the  one  case, 
it  must  be  in  the  other — which  is  absurd.  Or  else  the  logical  absurdity 
is  involved  of  inventing  one  cause  to  explain  an  effect  today  and  a 
wholly  different  cause  to  explain  the  same  effect  tomorrow.  This  is 
unjustifiable  in  any  case,  and  it  is  particularly  so  when  the  single  cause 
that  explains  both  cases  is  so  evident.  If  weak  heredity  causes  high 
mortality  in  the  royal  families,  why,  similarly,  cannot  weak  heredity 
cause  high  infant  mortality  in  the  industrial  communities  ?  We 
believe  it  does  account  for  much  of  it,  and  that  the  inadequate  income 
and  low  standard  of  living  are  largely  the  consequence  of  inferior 
heredity,  mental  as  well  as  physical.  The  parents  in  the  Genealogical 
Record  Ofiice  files  had,  many  of  them,  inadequate  incomes  and  low 
standards  of  living  under  frontier  conditions,  but  their  children  grew 
up  while  those  of  the  royal  families  were  dying  in  spite  of  every 
attention  that  wealth  could  command  and  science  could  furnish. 

If  the  infant  mortality  problem  is  to  be  solved  on  the  basis  of 
knowledge  and  reason,  it  must  be  recognized  that  sanitation  and 
hygiene  cannot  take  the  place  of  eugenics  any  more  than  eugenics 
can  dispense  with  sanitation  and  hygiene.  It  must  be  recognized  that 
the  death-rate  in  childhood  is  largely  selected,  and  that  the  most 
effective  way  to  cut  it  down  is  to  endow  the  children  with  better 
constitutions.  This  cannot  be  done  solely  by  any  euthenic  cam- 
paign; it  cannot  be  done  by  swatting  the  fly,  abolishing  the  mid-wife, 
sterilizing  the  milk,  nor  by  any  of  the  other  panaceas  sometimes 
proposed. 

But,  it  may  be  objected,  this  discussion  ignores  the  actual  facts. 
Statistics  show  that  infant  mortality  campaigns  have  consistently 
produced  reductions  in  the  death-rate.  The  figures  for  New  York, 
which  could  be  matched  in  dozens  of  other  cities,  show  that  the  num- 
ber of  deaths  per  1,000  births,  in  the  first  year  of  life,  has  steadily 
declined  since  a  determined  campaign  to  ''Save  the  Babies"  was 
started: 

1902 181        1909 1 29 

1903 152        1910 125 

1904 162        1911 112 

1905 159        1912 105 

1906 153        1913 102 

1907 144        1914 95 

1908 128 


EUGENICS  AND  EUTHENICS  493 

To  one  who  cannot  see  beyond  the  immediate  consequences  of  an 
action,  such  figures  as  the  above  indeed  give  quite  a  different  idea  of 
the  effects  of  an  infant  mortaUty  campaign,  than  that  which  we  have 
just  tried  to  create.  And  it  is  a  great  misfortune  that  euthenics  so 
often  fails  to  look  beyond  the  immecHate  effect,  fails  to  see  what 
may  happen  next  year,  or  10  years  from  now,  or  in  the  next  generation. 

We  admit  that  it  is  possible  to  keep  a  lot  of  children  alive  who 
would  otherwise  have  died  in  the  ffrst  few  months  of  life.  It  is  being 
done,  as  the  New  York  figures,  and  pages  of  others  that  could  be 
cited,  prove.     The  ultimate  result  is  twofold: 

1.  Some  of  those  who  are  doomed  by  heredity  to  a  selective  death, 
but  are  kept  alive  through  the  first  year,  die  in  the  second  or  third  or 
fourth  year.  They  must  die  sooner  or  later;  they  have  not  inherited 
sufficient  resistance  to  survive  more  than  a  limited  time.  If  they  are 
by  a  great  effort  carried  through  the  first  year,  it  is  only  to  die  in  the 
next.  This  is  a  statement  which  we  have  nowhere  observed  in  the 
propaganda  of  the  infant  mortality  movement;  and  it  is  perhaps  a 
disconcerting  one.  It  can  only  be  proved  by  refined  statistical 
methods,  but  several  independent  determinations  by  the  English 
biometricians  leave  no  doubt  as  to  the  fact.  This  work  of  Karl 
Pearson,  E.  C.  Snow,  and  Ethel  M.  Elderton,  was  cited  in  our  chapter 
on  natural  selection;  the  reader  will  recall  how  they  showed  that 
nature  is  weeding  out  the  weaklings,  and  in  proportion  to  the  strin- 
gency with  which  she  weeds  them  out  at  the  start,  there  are  fewer 
weaklings  left  to  die  in  succeeding  years. 

To  put  the  facts  in  the  form  of  a  truism,  part  of  the  children  born 
in  any  district  in  a  given  year  are  doomed  by  heredity  to  an  early 
death;  and  if  they  die  in  one  year  they  will  not  be  alive  to  die  in  the 
succeeding  year,  and  vice  versa.  Of  course  there  are  in  addition 
infant  deaths  which  are  not  selective  and  which  if  prevented  would 
leave  the  infant  with  as  good  chance  as  any  to  live. 

In  the  light  of  these  researches,  we  are  forced  to  conclude  that 
baby-saving  campaigns  accomplish  less  than  is  thought;  that  the 
supposed  gain  is  to  some  extent  temporary  and  illusory. 

2.  There  is  still  another  consequence.  If  the  gain  is  by  great 
exertions  made  more  than  temporary;  if  the  baby  who  would  other- 
wise have  died  in  the  first  months  is  brought  to  adult  life  and  repro- 
duction, it  means  in  many  cases  the  dissemination  of  another  strain 
of  weak  heredity,  which  natural  selection  would  have  cut  off  ruthlessly 


494      READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

in  the  interests  of  race  betterment.  In  so  far,  then,  as  the  infant 
mortahty  movement  is  not  futile  it  is,  from  a  strict  biological  view- 
point, often  detrimental  to  the  future  of  the  race. 

Do  we  then  discourage  all  attempts  to  save  the  babies  ?  Do  we 
leave  them  all  to  natural  selection ?  Do  we  adopt  the  ''better  dead" 
gospel  ? 

Unqualifiedly,  no!  The  sacrifice  of  the  finer  human  feelings, 
which  would  accompany  any  such  course,  would  be  a  greater  loss  to 
the  race  than  is  the  eugenic  loss  from  the  perpetuation  of  weak  strains 
of  heredity.  The  abolition  of  altruistic  and  humanitarian  sentiment 
for  the  purpose  of  race  betterment  would  ultimately  defeat  its  own  end 
by  making  race  betterment  impossible. 

But  race  betterment  will  also  be  impossible  unless  a  clear  distinc- 
tion is  made  between  measures  that  really  mean  race  betterment  of  a 
fundamental  and  permanent  nature,  and  measures  which  do  not. 

We  have  chosen  the  Infant  Mortality  Movement  for  analysis  in  this 
chapter  because  it  is  an  excellent  example  of  the  kind  of  social  better- 
ment which  is  taken  for  granted,  by  most  of  its  proponents,  to  be  a 
fundamental  piece  of  race  betterment;  but  which,  as  a  fact,  often 
means  race  impairment.  No  matter  how  abundant  and  urgent  are 
the  reasons  for  continuing  to  reduce  infant  mortality  wherever  pos- 
sible, it  is  dangerous  to  close  the  eyes  to  the  fact  that  the  gain  from  it 
is  of  a  kind  that  must  be  paid  for  in  other  ways;  that  to  carry  on  the 
movement  without  adding  eugenics  to  it  will  be  a  short-sighted  policy, 
which  increases  the  present  happiness  of  the  world  at  the  cost  of 
diminishing  the  happiness  of  posterity  through  the  perpetuation  of 
inferior  strains. 

While  some  euthenic  measures  are  eugenically  evils,  even  if 
necessary  ones,  it  must  not  be  inferred  that  all  euthenic  measures  are 
dysgenic.  Many  of  them,  such  as  the  economic  and  social  changes  we 
have  suggested  in  earlier  chapters,  are  an  important  part  of  eugenics. 
Every  euthenic  measure  should  be  scrutinized  from  the  evolutionary 
standpoint;  if  it  is  eugenic  as  well  as  euthenic,  it  should  be  whole- 
heartedly favored;  if  it  is  dysgenic  but  euthenic  it  should  be  con- 
demned or  adopted,  according  to  whether  or  not  the  gain  in  all  ways 
from  its  operation  will  exceed  the  damage. 

In  general,  euthenics,  when  not  accompanied  by  some  form  of 
selection  (i.e.,  eugenics)  ultimately  defeats  its  own  end.  If  it  is  accom- 
panied by  rational  selection,  it  can  usually  be  indorsed.     Eugenics, 


EUGENICS  AND  EUTHENlCS  495 

on  the  other  hand,  is  hkewise  inadequate  unless  accompanied  by 
constant  improvement  in  the  surroundings;  and  its  advocates  must 
demand  euthenics  as  an  accompaniment  of  selection,  in  order  that  the 
opportunity  for  getting  a  fair  selection  may  be  as  free  as  possible.  If 
the  euthenist  likewise  takes  pains  not  to  ignore  the  existence  of  the 
racial  factor,  then  the  two  schools  are  standing  on  the  same  ground, 
and  it  is  merely  a  matter  of  taste  or  opportunity,  whether  one  empha- 
sizes one  side  or  the  other.  Each  of  the  two  factions,  sometimes 
thought  to  be  opposing,  will  be  seen  to  be  getting  the  same  end  result, 
namely,  human  progress. 

Not  only  are  the  two  schools  working  for  the  same  end,  but  each 
must  depend  in  still  another  way  upon  the  other,  in  order  to  make 
headway.  The  eugenist  cannot  see  his  measures  put  into  effect  except 
through  changes  in  law  and  custom — i.e.,  euthenic  changes.  He  must 
and  does  appeal  to  euthenics  to  secure  action.  The  social  reformer,  on 
the  other  hand,  cannot  see  any  improvements  made  in  civilization 
except  through  the  discoveries  and  inventions  of  some  citizens  who  are 
inherently  superior  in  abihty.  He  in  turn  must  depend  on  eugenics 
for  every  advance  that  is  made. 

It  may  make  the  situation  clearer  to  state  it  in  the  customary 
terms  of  biological  philosophy.  Selection  does  not  necessarily  result 
in  progressive  evolution.  It  merely  brings  about  the  adaptation  of 
a  species  or  a  group  to  a  given  environment.  The  tapeworm  is  the 
stock  example.  In  human  evolution,  the  nature  of  this  environment 
will  determine  whether  adaptation  to  it  means  progress  or  retro- 
gression, whether  it  leaves  a  race  happier  and  more  productive,  or  the 
reverse.  All  racial  progress,  or  eugenics,  therefore,  depends  on  the 
creation  of  a  good  environment,  and  the  fitting  of  the  race  to  that 
environment.  Every  improvement  in  the  en\dronment  should  bring 
about  a  corresponding  biological  adaptation.  The  two  factors  in 
evolution  must  go  side  by  side,  if  the  race  is  to  progress  in  what  the 
human  mind  considers  the  direction  of  advancement.  In  this  sense, 
euthenics  and  eugenics  bear  the  same  relation  to  human  progress  as 
a  man's  two  legs  do  to  his  locomotion. 

Social  workers  in  purely  euthenic  fields  have  frequently  failed  to 
remember  this  progress  of  adaptation,  in  their  efforts  to  change  the 
environment.  Eugenists,  in  centering  their  attention  on  adaptation, 
have  sometimes  paid  too  little  attention  to  the  kind  of  environment  to 
which  the  race  was  being  adapted.     The  present  book  holds  tliat  the 


496     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

second  factor  is  just  as  important  as  the  first,  for  racial  progress;  that 
one  leg  is  just  as  important  as  the  other,  to  a  pedestrian.  Its  only  con- 
flict with  euthenics  appertains  to  such  euthenic  measures  as  impair  the 
adaptability  of  the  race  to  the  better  environment  they  are  trying  to 
make. 

Some  supposedly  euthenic  measures  opposed  by  eugenics  are  not 
truly  euthenic,  as  for  instance  the  limitation  of  a  superior  family  in 
order  that  all  may  get  a  college  education.  For  these  spurious 
euthenic  measures,  something  truly  euthenic  should  be  substituted. 
Measures  which  show  a  real  conflict  may  be  typified  by  the  infant 
mortality  movement.  There  can  be  no  doubt  but  that  sanitation  and 
hygiene,  prenatal  care  and  inteUigent  treatment  of  mothers  and  babies, 
are  truly  euthenic  and  desirable.  At  the  same  time,  as  has  been 
shown,  these  euthenic  measures  result  in  the  survival  of  inferior 
children,  who  directly  or  through  their  posterity  will  be  a  drag  on  the 
race.  Euthenic  measures  of  this  type  should  be  accompanied  by 
counterbalancing  measures  of  a  more  eugenic  character. 

Barring  these  two  types,  euthenics  forms  a  necessary  concomitant 
of  the  eugenic  program;  and,  as  we  have  tried  to  emphasize,  eugenics 
is  likewise  necessary  to  the  complete  success  of  every  euthenic  program. 
How  foohsh,  then,  is  antagonism  between  the  two  forces!  Both  are 
working  toward  the  same  end  of  human  betterment,  and  neither  can 
succeed  without  the  other.  When  either  attempts  to  eliminate  the 
other  from  its  work,  it  ceases  to  advance  toward  its  goal.  In  which 
camp  one  works  is  largely  a  matter  of  taste.  If  on  a  road  there  is  a 
gradient  to  be  leveled,  it  will  be  brought  down  most  quickly  by  two 
parties  of  workmen,  one  cutting  away  at  the  top,  and  the  other  filling 
in  the  bottom.  For  the  two  parties  to  indulge  in  mutual  scorn  and 
recrimination  would  be  no  more  absurd  than  for  eugenics  and  euthenics 
to  be  put  in  opposition  to  each  other.  The  only  reason  they  have  been 
in  opposition  is  because  some  of  the  workers  did  not  clearly  understand 
the  nature  of  their  work.  With  the  dissemination  of  a  knowledge  of 
biology,  this  ground  of  antagonism  will  disappear. 


chapi1':r  xxxmi 
the  promise  of  race  culture' 

CALEB   WILLIAMS   S^VLEEBY 

Tlie  best  is  yet  to  be. 

In  its  form  of  what  we  have  called  negative  eugenics,  the  practice 
of  our  principle  would  assuredly  reduce  to  an  incalculable  extent  the 
amount  of  human  defect,  mental  and  physical,  which  each  generation 
now  exhibits.  This  alone,  as  has  been  said,  would  be  far  more  than 
sufficient  to  justify  us.  A  world  without  hereditary  disease  of  mind 
and  body  would  alone  warrant  the  hint  of  Ruskin  that  posterity  may 
some  day  look  back  upon  us  with  "  incredulous  disdain."  Yet,  assum- 
ing that  this  could  be  accomplished,  as  it  will  be  accomplished,  what 
more  is  to  be  hoped  for  ?  Must  race-culture  cease  merely  when  it  has 
raised  the  average  of  the  community  by  reducing  to  a  minimum  the 
proportion  of  those  who  are  thus  grossly  defective  in  mind  or  body  ? 
Such  disease  apart,  are  we  to  be  content,  must  we  be  content,  with 
the  present  level  of  mediocrity  in  respect  of  intelligence  and  temper 
and  moral  sentiment  ?  Can  we  anticipate  a  London  in  which  the 
present  ratio  of  musical  comedy  to  great  opera  will  be  reversed,  in 
which  the  works  of  Mr.  George  Meredith  will  sell  in  hundreds  of 
thousands,  whilst  some  of  our  popular  novelists  will  have  to  find  other 
means  of  earning  a  living  ?  Can  we  make  for  a  critical  democracy 
which  no  political  party  can  fool,  and  which  will  choose  its  best  to 
govern  it  ?  Yet  more,  can  we  undertake,  now  or  hereafter,  to  provide 
every  generation  with  its  own  Shakespeare  and  Beethoven  and 
Tintoretto  and  Newton  ?  What,  in  a  word,  is  the  promise  of  positive 
eugenics?  It  is  to  this  aspect  of  the  question  that  Mr.  Galton  has 
mainly  directed  himself.  Indeed  he  was  led  to  formulate  the  princi- 
ples and  ideals  of  the  new  science  by  his  study  of  hereditary  genius 
some  four  decades  ago.  Let  us  now  attempt  to  answer  some  of  these 
questions. 

The  production  of  genius. — And  first  as  to  the  production  of 
genius.  It  is  this,  perhaps,  that  has  been  the  main  butt  of  the  jesters 
who  pass  for  philosophers  with  some  of  us  today.     It  may  be  said 

^  From  C.  W.  Saleeby,  Parenthood  and  Race  Culture  (copyright  1909).  Used  by 
special  permission  of  the  publishers,  MolTat,  Yard,  and  Company. 

497 


498      READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

at  once  that  neither  Mr.  Galton  nor  any  other  responsible  person  has 
ever  asserted  that  we  can  produce  genius  at  will.  The  difficulties  in 
the  way  of  such  a  project — at  present — are  almost  innumerable. 
One  or  two  may  be  cited. 

In  the  first  place,  there  is  the  cardinal — but  by  no  means  univer- 
sal— difficulty  that  the  genius  is  too  commonly  so  occupied  with  the 
development  and  expansion  of  his  own  individuality  that  he  has  little 
time  or  energy  for  the  purposes  of  the  race.  This,  of  course,  is  an 
example  of  Spencer's  great  generalization  as  to  the  antagonism  or 
inverse  ratio  between  individuation  and  genesis. 

Again,  there  is  the  generalization  of  heredity  formulated  by 
Mr.  Galton,  and  named  by  him  the  law  of  regression  towards  mediocrity. 
It  asserts  that  the  children  of  those  who  are  above  or  below  the  mean  of 
a  race,  tend  to  return  towards  that  mean.  The  children  of  the  born 
criminal  will  be  probably  somewhat  less  criminal  in  tendency  than  he, 
though  more  criminal  than  the  average  citizen.  The  children  of  the 
man  of  genius,  if  he  has  any,  will  probably  be  nearer  mediocrity  than 
he,  though  on  the  average  possessing  greater  talent  than  the  average 
citizen.  It  is  thus  not  in  the  nature  of  sheer  genius  to  reproduce  on  its 
own  level.  It  is  only  the  critics  who  are  totally  ignorant  of  the  elemen- 
tary facts  of  heredity  that  attribute  to  the  eugenist  an  expectation  of 
which  no  one  knows  the  absurdity  so  well  as  he  does. 

On  the  other  hand,  it  is  impossible  to  question  that  the  hereditary 
transmission  of  genius  or  great  talent  does  occur.  One  may  cite  at 
random  such  cases  as  that  of  the  Bach  family,  Thomas  and  Matthew 
Arnold,  James  and  John  Stuart  Mill;  and  the  reader  who  is  inclined 
to  believe  that  there  is  no  law  or  likelihood  in  this  matter,  must 
certainly  make  himself  acquainted  with  Mr.  Galton's  Hereditary 
Genius,  and  with  such  a  paper  as  that  which  he  printed  in  Sociological 
Papers,  1904,  furnishing  an  "index  to  achievements  of  near  kinsfolk 
of  some  of  the  Fellows  of  the  Royal  Society."  There  is,  of  course,  the 
obvious  fallacy  involved  in  the  possibility  that  not  heredity  but 
environment  was  really  responsible  for  many  of  these  cases.  It  must 
have  been  a  great  thing  to  have  such  a  father  as  James  Mill.  But  it 
would  be  equally  idle  to  imagine  that  the  evidence  can  be  dismissed 
with  this  criticism.  A  Matthew  Arnold,  a  John  Stuart  Mill,  could  not 
be  manufactured  out  of  any  chance  material  by  an  ideal  education 
continued  for  a  thousand  years. 

The  transmission  of  genius. — One  single  instance  of  the  trans- 
mission of  genius  or  great  talent  in  a  family  may  be  cited.     We  shall 


THE  PROMISE  OF  RACE  CULTURE  499 

take  the  family  which  produced  Charles  Darwin,  the  discoverer  of  the 
fundamental  principle  of  eugenics,  and  his  first  cousin,  Francis  Galton. 
Darwin's  grandfather  was  Erasmus  Darwin,  physician,  poet  and 
philosopher,  and  independent  expounder  of  the  doctrine  of  organic 
evolution.  Darwin's  father  was  a  distinguished  physician,  described 
by  his  son  as  ''the  wisest  man  I  ever  knew."  Darwin's  maternal 
grandfather  was  Josiah  Wedgwood,  the  famous  founder  of  the  pottery 
works.  Amongst  his  first  cousins  is  Mr.  Francis  Galton.  He  has  five 
living  sons,  each  a  man  of  great  distinction,  including  Mr.  Francis 
Darwin  and  Sir  George  Darwin,  both  of  them  original  thinkers, 
honored  by  the  presidency  of  the  British  Association.  No  one  will 
put  such  a  case  as  this  down  to  pure  chance  or  to  the  influence  of 
environment  alone.  This  is  evidently,  like  many  others,  a  greatly 
distinguished  stock.  The  worth  of  such  families  to  a  nation  is  wholly 
beyond  any  one's  powers  of  estimation.  W'liat  if  Erasmus  Darwin 
had  never  married! 

No  student  of  human  heredity  can  doubt  that,  however  limited 
our  immediate  hopes,  facts  such  as  those  alluded  to  furnish  promise 
of  great  things  for  the  future.  But  let  us  turn  now  from  genius  to 
what  we  usually  call  talent. 

The  production  of  talent. — There  can  be  no  question  that  amongst 
the  promises,  of  race-culture  is  the  possibility  of  breeding  such  things 
as  talent  and  the  mental  energy  upon  which  talent  so  largely  depends. 
In  the  Inquiries  into  Human  Faculty,  Mr.  Galton  shows  the  remark- 
able extent  to  which  energy  or  the  capacity  for  labor  underlies  intellec- 
tual achievement.     He  says,  of  energy: 

''It  is  consistent  with  all  the  robust  virtues,  and  makes  a  large 
practice  of  them  possible.  It  is  the  measure  of  fullness  of  life ;  the  more 
energy  the  more  abundance  of  it;  no  energy  at  all  is  death;  idiots  are 
feeble  and  listless.  In  the  enquiries  I  made  on  the  antecedents  of  men 
of  science  no  points  came  out  more  strongly  than  that  the  leaders  of 
scientific  thought  were  generally  gifted  with  remarkable  energy,  and 
that  they  had  inherited  the  gift  of  it  from  their  parents  and  grand- 
parents  It  m.aybe  objected  that  if  the  race  were  too  healthy  and 

energetic  there  would  be  insufficient  call  for  the  exercise  of  the  jiilying 
and  self-denying  virtues,  and  the  character  of  men  would  grow  harder 
in  consequence.  But  it  does  not  seem  reasonable  to  preserve  sickly 
breeds  for  the  sole  purpose  of  tending  them,  as  the  breed  of  foxes  is 
preserved  solely  for  sport  and  its  attendant  advantages.  There  is 
little  fear  that  misery  will  ever  cease  from  the  land,  or  that  the 


500     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

compassionate  will  fail  to  find  objects  for  their  compassion;  but  at 
present  the  supply  vastly  exceeds  the  demand ;  the  land  is  over-stocked 
and  over-burdened  with  the  listless  and  the  incapable.  In  any  scheme 
of  eugenics,  energy  is  the  most  important  quality  to  favor;  it  is,  as  we 
have  seen,  the  basis  of  living  action,  and  it  is  eminently  transmissible 
by  descent." 

Need  it  be  pointed  out  that  any  political  system  which  ceases  to 
favor  or  actively  disfavors  energy,  making  it  as  profitable  to  be  lazy  as 
to  be  active,  is  antieugenic,  and  must  inevitably  lead  to  disaster  ? 
That,  however,  by  the  way.  Our  present  point  is  that  eugenics  can 
reasonably  promise,  when  its  principles  are  recognized,  to  multiply 
the  human  and  diminish  the  vegetable  type  in  the  community.  In  so 
doing,  it  will  greatly  further  the  production  of  talent,  and  therefore 
of  that  traditional  or  acquired  progress  which  men  of  talent  and 
genius  create.  Such  a  result  will  also  further,  though  indirectly,  the 
production  of  genius  itself.  For,  as  Mr.  Galton  points  out,  "men  of  an 
order  of  ability  which  is  now  very  rare,  would  become  more  frequent, 
because  the  level  out  of  which  they  rose  would  itself  have  risen." 

This  is  by  no  means  the  only  fashion  in  which  an  effective  and 
practicable  race-culture  would  serve  genius,  and  I  shall  not  be  blamed 
for  considering  this  matter  further  by  any  reader  who  realizes,  however 
faintly,  what  the  man  of  genius  is  worth  to  the  world.  If  it  were  shown 
possible  to  establish  such  social  conditions  that  genius  could  never 
flower  in  them,  we  should  realize  that  their  establishment  would 
mean  the  putting  of  an  end  to  progress  and  the  blasting  of  all  the 
highest  hopes  of  the  highest  of  all  ages. 

The  immediate  need  of  this  age,  as  of  all  ages,  is  perhaps  not  so 
much  the  birth  of  babies  capable  of  developing  into  men  and  women  of 
genius,  as  the  full  exploitation  of  the  possibilities  of  genius  with  which, 
as  I  fancy,  every  generation  on  the  average  is  about  as  well  endowed  as 
any  other.  There  is,  of  course,  the  popular  doctrine  that  there  are  no 
mute  inglorious  Miltons,  that  "genius  will  out,"  and  that  therefore 
if  it  does  not  appear,  it  is  not  there  to  appear.  In  expressing  the  com- 
pelling power  of  genius  in  many  cases  this  doctrine  is  not  without 
truth.  Yet  history  abounds  in  instances  where  genius  has  been  de- 
stroyed by  environment — and  we  can  only  guess  how  many  more 
instances  there  are  of  which  history  has  no  record.  To  take  the  single 
case  of  musical  genius,  it  is  a  lamentable  thought  that  there  may  be 
those  now  living  whose  natural  endowments,  in  a  favorable  environ- 
ment, would  have  enabled  them  to  write  symphonies  fit  to  place 


THE  PROMISE  OF  RACE  CULTURi:  501 

beside  Beethoven's,  but  whom  some  environmental  factors — conven- 
tional, economic,  educational,  or  what  not — have  silenced;  or  worse, 
have  persuaded  to  write  such  sterile  nullities  as  need  not  here  be 
instanced.  There  is  surely  no  waste  in  all  this  wasteful  world  so 
lamentable  as  this  waste  of  genius. 

If,  then,  anyone  could  devise  for  us  a  means  by  which  the  genius, 
potentially  existing  at  any  time,  were  realized,  he  would  have  per- 
formed in  effect  a  service  equivalent  to  that  of  which  eugenics  rei)udi- 
ates  the  present  possibility — the  actual  creation  of  genius.  But  if  we 
consider  what  the  conditions  are  which  cause  the  waste  of  genius,  we 
realize  at  once  that  they  mainly  inhere  in  the  level  of  the  human 
environment  of  the  priceless  potentiality  in  question.  As  we  noted 
elsewhere,  in  an  age  like  that  of  Pericles  genius  springs  up  on  all  hands. 
It  is  encouraged  and  welcomed  because  the  average  level  of  the  human 
environment  in  which  it  finds  itself  is  so  high.  But  if  eugenics  can 
raise  the  average  level  of  intelligence,  in  so  doing  not  merely  does  it 
render  more  likely,  as  Mr.  Galton  points  out,  the  production  of  men  of 
the  highest  abiHty,  but  it  provides  those  conditions  in  which  men  of 
genius,  now  swamped,  can  swim.  We  could  not  undertake  to  produce 
a  Shakespeare,  but  we  might  reasonably  hope  to  produce  a  generation 
which  would  not  destroy  its  Shakespeares.  And  even  if  men  of  genius 
still  found  it  necessary,  as  men  of  genius  have  found  it  necessary,  to 
"play  to  the  gallery,"  they  would  play,  as  IVIr.  Galton  says  of  the 
demagogue  in  a  eugenic  age,  "to  a  more  sensible  gallery  than  at 
present." 

Darwin  somewhere  points  out  that  it  is  not  the  scientific,  but  the 
unscientific  man  who  denies  future  possibihties.  Thus  though  an 
advocate  of  eugenics  may  be  applauded  for  his  judgment  if  he  declares 
that  the  creation  of  genius  will  forever  be  impossible,  yet  I  should  not 
care  to  assert  that  the  ultimate  limitations  of  eugenics  can  thus  be 
defined.     We  have  yet  to  hear  the  last  of  IMendelism. 

Eugenics  and  unemployment. — Let  us  look  now  at  another  aspect 
of  the  promise  of  race-culture.  When  the  time  comes  that  quality 
rather  than  quantity  is  the  ideal  of  those  who  concern  themselves  with 
the  population  question,  it  is  quite  evident  that  not  a  few  of  the  social 
problems  which  we  now  find  utterly  insoluble  will  disapjx^ar.  In 
this  brief  outline,  we  can  only  allude  to  one  or  two  points.  Take,  for 
instance,  the  question  of  unemployment.  We  know  that  some  by  no 
means  small  proportion  of  the  unem}:)loyed  were  really  destined  to  be 
unemployable  from  the  first,  as  for  instance  by  reason  of  hereditary 


502      READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

disease.  It  were  better  for  them  and  for  us  that  they  had  never  been 
born.  Many  more  of  the  unemployed  have  been  made  unemployable 
by  the  influence  of  over-crowding,  to  which  they  were  subjected  in  their 
years  of  development.  Is  there,  can  there  be,  any  real  and  permanent 
remedy  for  overcrowding,  but  the_erection  of  parenthood  into  an  act 
of  personal  and  provident  responsibility  ? 

Eugenics  and  woman. — Take,  again,  the  woman  question.  No 
one  will  deny  that  in  many  of  its  gravest  forms,  especially  in  its 
economic  form,  and  the  question  of  the  employment  of  women,  wisely 
or  horribly,  this  depends  (to  a  degree  which  few,  I  think,  realize)  upon 
the  fact  that  there  are  now  (1909),  for  instance,  1,300,000  women  in 
excess  in  this  country.  Is  it  then  proposed,  the  reader  will  say,  by 
means  of  race-culture  to  exterminate  the  superfluous  woman  ?  Indeed, 
no.  But  is  the  reader  aware  that  Nature  is  not  responsible  for  the 
existence  of  the  superfluous  woman  ?  There  are  more  boys  than  girls 
born  in  the  ratio  of  about  103  or  104  to  100;  and  Nature  means  them  all 
to  live,  boys  and  girls  alike.  If  they  did  so  live,  we  should  have  merely 
the  problem  of  the  superfluous  man,  which  would  not  be  an  economic 
problem  at  all.  But  we  destroy  hosts  of  all  the  children  that  are  born, 
and  since  male  organisms  are  in  general  less  resistant  than  female 
organisms,  we  destroy  a  disproportionate  number  of  boys,  so  that  the 
natural  balance  of  the  sexes  is  inverted.  Unlike  ancient  societies  we 
largely  practice  male  infanticide.  Can  the  reader  beheve  that  there 
is  any  permanent  and  final  means  of  arresting  this  wastage  of  child- 
life,  with  its  singular  and  far-reaching  consequences,  other  than  the 
elevation  of  parenthood,  wholly  apart  from  the  question  of  the  selec- 
tion of  parents  ?  We  shall  not  succeed  in  keeping  all  the  children  alive 
(with  a  trivial  number  of  exceptions),  thereby  abolishing  the  super- 
fluous woman  by  keeping  alive  the  boy  who  should  have  grown  up  to 
be  her  partner,  until  we  greatly  reduce  the  birth-rate;  as  it  must  and 
will  be  reduced  when  the  ideal  of  race-culture  is  realized,  and  no  child 
comes  into  the  world  that  is  not  already  loved  and  desired  in  antici- 
pation. 

Eugenics  and  cruelty  to  children. — ^This  ideal,  also,  offers  us  in 
its  realization  the  only  complete  remedy  for  the  present  ghastly  cruelty 
under  which  so  many  children  suffer  even  in  Great  Britain,  even  in  the 
twentieth  century.  Is  the  reader  aware  that  the  National  Society 
for  the  Prevention  of  Cruelty  to  Children  inquired  into  the  ill-treat- 
ment or  cruel  neglect  of  115,000  children  in  the  year  beginning  April 
I  St,  1906  ?     It  has  been  reasonably  and  carefully  estimated  that  "  over 


THE  PROMISE  OF  RACE  CULTURE  503 

half  a  million  children  are  involved  in  the  total  of  the  wastage  of  child- 
life  and  the  torture  and  neglect  of  child-Ufe  in  a  single  year."  Surely 
Mr.  G.  R.  Sims,  to  whom  I  would  olTer  a  hearty  tribute  for  his  recent 
services  to  childhood,  is  justified  in  saying,  "Against  the  guilt  of  race 
suicide  our  men  of  science  are  everywhere  preaching  their  sermons 
to-day.  It  is  against  the  guilt  of  race  murder  that  the  cry  of  the 
children  should  ring  through  the  land."  As  regards  race  suicide  and 
the  men  of  science,  I  am  not  so  sure  as  to  the  assertion.  But  the  truth 
of  the  second  sentence  quoted  is  as  indisputable  as  it  is  horriljle. 

Now  no  legislation  conceivable  will  wholly  cure  this  evil  nor  avert 
its  consequences.  At  bottom  it  depends  upon  human  nature,  and 
you  can  cure  it  only  by  curing  the  defect  of  human  nature.  This,  in 
general,  is  of  course  beyond  the  immediate  powers  of  man,  but  evi- 
dently we  should  gain  the  same  end  if  only  we  could  confme  the  advent 
of  children  to  those  parents  who  desired  them — that  is  to  say,  those  in 
whom  human  nature  displayed  the  first,  if  not  indeed  almost  the  only, 
requisite  for  the  happiness  of  childhood.  To  this  most  beneficent 
and  wholly  moral  end  we  shall  come,  notwithstandin'g  the  blind  and 
pitiable  guidance  of  most  of  our  accredited  moral  teachers  today.  By 
no  other  means  than  the  realization  of  the  ideal  defined,  that  every 
new  baby  shall  be  loved  and  desired  in  anticipation — an  ideal  which  is 
perfectly  practicable — can  the  black  stain  of  child  murder  and  child 
torture  and  child  neglect  be  removed  from  our  civilization. 

Ruskin  and  race-culture. — The  name  of  Ruskin,  perhaps,  would 
not  occur  to  the  reader  as  likely  to  afford  support  to  the  fair  hopes  of 
the  eugenist.     Consider  then,  these  words  from  Time  and  Tide: 

"You  leave  your  marriages  to  be  settled  by  supply  and  demand, 
instead  of  wholesome  law.  And  thus,  among  your  youths  and  maid- 
ens, the  improvident,  incontinent,  selfish,  and  foolish  ones  marry, 
whether  you  will  or  not;  and  beget  families  of  children  necessarily 
inheritors  in  a  great  degree  of  these  parental  dispositions;  and  for 
whom,  supposing  they  had  the  best  dispositions  in  the  world,  you  have 
thus  provided,  by  way  of  educators,  the  foolishest  fathers  and  mothers 
you  could  find;  (the  only  rational  sentence  in  their  letters,  usually,  is 
the  invariable  one,  in  which  they  declare  themselves  'incapable  of 
providing  for  their  children's  education').  On  the  other  hand,  who- 
soever is  wise,  patient,  unselfish,  and  pure  among  your  youth,  you 
keep  maid  or  bachelor;  wasting  their  best  days  of  natural  life  in  j^ain- 
ful  sacrifice,  forbidding  them  their  best  help  and  best  reward,  and  care- 
fully excluding  their  prudence  and  tenderness  from  any  ofiices  of 


504      READINGS  IN  E\^OLUTION,  GENETICS,  AND  EUGENICS 

parental  duty.  Is  not  this  a  beatific  and  beautifully  sagacious  system 
for  a  Celestial  Empire,  such  as  that  of  these  British  Isles?" 

Apart  from  the  point  as  to  wholesome  law  rather  than  the  educa- 
tion of  opinion  as  the  eugenic  means,  the  foregoing  passage  must  win 
the  assent  and  respect  of  every  eugenist.  It  indicates  the  promise  of 
race-culture  as  it  appeared  to  John  Ruskin.  The  passage  has  been 
quoted  in  full,  not  for  the  benefit  of  the  ordinary  thoughtful  reader  but 
for  that  of  the  professional  literary  man  who,  in  this  remarkable  age, 
so  far  as  I  can  judge,  reads  nothing  but  what  he  writes,  and  thus  quali- 
fies himself  for  dismissing  Spencer  or  Darwin  or  Galton  by  any  casual 
phrase. 

Race-culture  and  human  variety. — Now  let  us  turn  to  another 
question.  Let  it  be  asserted  most  emphatically  that,  if  there  is  any- 
thing in  the  world  which  eugenics  or  race-culture  does  not  promise  or 
desire,  it  is  the  production  of  a  uniform  type  of  man.  This  delusion, 
for  which  there  has  never  been  any  warrant  at  all,  possesses  many  of 
the  critics  of  eugenics,  and  they  have  made  pretty  play  with  it,  just 
as  they  do  with  their  other  delusions.  Let  us  note  one  or  two  facts 
which  bear  upon  this  most  undesirable  ideal. 

In  the  first  place,  it  is  unattainable  because  of  the  existence  of 
what  we  call  variation.  No  apparatus  conceivable  would  suffice  to 
eliminate  from  every  generation  those  who  varied  from  the  accepted 
type. 

In  the  second  place,  this  uniformity  is  supremely  undesirable  from 
the  purely  evolutionary  point  of  view,  because  its  attainment  would 
mean  the  arrest  of  all  progress.  All  organic  evolution,  as  we  know, 
depends  upon  the  struggle  between  creatures  possessing  various  varia- 
tions and  the  consequent  selection  of  those  variations  which  con- 
stitute their  possessors  best  adapted  or  fitted  to  the  particular  environ- 
ment. If  there  is  no  variation  there  can  be  no  evolution.  To  aim  at 
the  suppression  of  variation,  therefore,  on  supposed  eugenic  grounds 
(which  would  be  involved  in  aiming  at  any  uniform  type  of  mankind) 
would  be  to  aim  at  destroying  the  necessary  condition  of  all  racial 
progress.  The  mere  fact  that  all  the  critics  of  race-culture  attribute 
to  evolutionists,  of  all  people,  the  desire  to  suppress  variation,  is  a 
pathognomonic  symptom  of  their  critical  quality. 

And,  of  course,  quite  independently  of  the  evolutionary  function  of 
variation — though  this  is  cardinal  and  must  never  be  forgotten  by  the 
politician  of  any  school,  since  what  we  call  individuality  is  variation 
on  the  human  plane — the  value  of  variation  in  ordinary  life  is  wholly 


THE  PROMISE  OF  RACE  CULTURE  505 

incalculable.  It  is  not  merely  that,  as  Mr.  Galton  says,  "There  are  a 
vast  number  of  conflicting  ideals,  of  alternative  characters,  of  incom- 
patible civilizations;  but  they  are  wanted  to  give  fullness  and  interest 
to  life.  Society  would  be  very  dull  if  every  man  resembled  the  highly 
estimable  Marcus  Aurelius  or  Adam  Bede."  The  question  is  not 
merely  as  to  the  interest  of  life.  Much  more  important  is  the  fact 
that  it  takes  all  sorts  to  make  a  world.  What  is  the  development  of 
society  but  the  result  of  the  psychological  division  of  labor  in  the  social 
organism  ?  And  how  could  such  division  of  labor  be  carried  out  if 
we  had  not  various  types  of  laborers?  What  would  be  the  good  of 
science  if  there  were  no  poetry  or  music  to  live  for?  How  would 
poetry  and  music  help  us  if  we  had  not  men  of  science  to  protect  our 
shores  from  plague  ?  Obviously  the  existence  of  men  of  most  various 
types  is  a  necessity  for  any  highly  organized  society.  Even  if  eugenics 
were  capable — as  it  is  not — of  producing  a  complete  and  balanced 
type,  fit  up  to  a  point  to  turn  out  a  satisfactory  poem,  a  satisfactory 
symphony  or  a  satisfactory  sofa,  the  utmost  could  not  be  expected  of 
such  a  man  in  any  of  these  directions.  In  a  word,  as  long  as  their 
activities  are  not  antisocial,  men  cannot  be  of  too  various  types.  We 
require  mystic  and  mathematician,  poet  and  pathologist.  Only,  we 
want  good  specimens  of  each.  ''The  aim  of  eugenics,"  says 
Mr.  Galton,  "is  to  represent  each  class  or  sect  by  its  best  specimens; 
that  done,  to  leave  them  to  work  out  their  common  civilization  in  their 

own  way Special  aptitudes  w^ould  be  assessed  highly  by  those 

who  possessed  them,  as  the  artistic  faculties  by  artists,  fearlessness 
of  inquiry  and  veracity  by  scientists,  rehgious  absorption  by  mystics, 
and  so  on.  There  would  be  self-sacrificers,  self-tormentors,  and 
other  exceptional  idealists."  But  at  least  it  is  better  to  have  good 
rather  than  bad  specimens  of  any  kind,  whatever  that  kind  may  be. 
Mr.  Galton  thinks  that  all  except  cranks  would  agree  as  to  including 
health,  energy,  ability,  manliness,  and  courteous  disposition  amongst 
quaUties  uniformly  desirable — alike  in  poet  and  pathologist.  We 
should  desire  also  uniformity  as  to  the  absence  of  the  antisocial 
proclivities  of  the  born  criminal.  So  much  uniformity  being  granted, 
let  us  have  with  it  the  utmost  conceivable  variety — more,  indeed, 
than  most  of  us  can  conceive. 

This  point,  of  course,  is  cardinal  from  the  point  of  view  of  jiracticc. 
No  progress  could  be  made  with  eugenics,  it  would  be  impossible  even 
to  form  a  Eugenics  Education  Society,  if  each  of  us  were  to  regard 
the  particular  type  he  belongs  to  as  the  ideal,  and  were  to  seek  merely 


5o6      READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

to  obtain  the  best  specimens  of  that  type.  The  doctrine  that  it  takes 
all  sorts  to  make  a  world — a  doctrine  very  hard  for  youth  to  learn,  yet 
unconsciously  learnt  by  all  who  are  capable  of  learning  at  all — must 
be  regarded  as  cardinal  truth  for  the  eugenist.  All  he  asks  for,  all  he 
is  wise  in  seeking,  is  good  specimens  rather  than  bad.  Poets  certainly 
but  not  poetasters;  jesters  certainly,  but  not  clever  fools. 

Time  and  its  treasure.— Taking  the  modern  estimates  of  the 
physicists,  we  are  assured  that  the  total  period  of  past  human  existence 
is  very  brief  compared  with  what  may  reasonably  be  predicted. 
Granted,  then,  practically  unlimited  time,  what  inherent  limits  are 
there  to  the  upward  development  of  man  as  a  moral  and  intellectual 
being?  Shall  we  answer  this  question  by  a  study  of  the  nature  of 
matter  ?  Plainly  not.  Shall  we  answer  it  by  a  study  of  the  nature 
of  mind  ?  Surely  not,  for  the  study  of  the  mind  cannot  inform  us  as 
to  what  mind  might  be.  One  source  of  guidance  alone  we  have,  and 
this  is  the  amazing  contrast  which  exists  between  the  mind  of  man  at 
its  highest,  and  mind  in  its  humblest  animal  forms;  or  shall  we  say 
even  between  the  highest  and  lowest  manifestations  of  mind  within 
the  human  species  ?  The  measureless  height  of  the  ascent  thus  indi- 
cated offers  us  no  warrant  for  the  conclusion  that,  as  we  stand  on  the 
heights  of  our  life,  our  "glimpse  of  a  height  that  is  higher"  is  only  a 
hallucination.     On  the  contrary. 

There  is  no  warrant  whatever  for  supposing  that  the  forces  which 
have  brought  us  thus  far  are  yet  exhausted ;  they  have  their  origin  in 
the  inexhaustible.  Who,  gazing  on  the  earth  of  a  hundred  million 
years  ago,  could  have  predicted  life — could  have  recognized,  in  the 
forces  then  at  work  and  the  matter  in  which  they  were  displayed,  the 
promise  and  potency  of  all  terrestrial  hfe  ?  Who,  contemplating  life 
at  a  much  later  stage,  even  later  mammalian,  could  have  seen  in  the 
simian  the  prophecy  of  man  ?  Who,  examining  the  earliest  nervous 
ganglia,  could  have  foreseen  the  human  cerebrum  ?  The  fact  that  we 
can  imagine  nothing  higher  than  ourselves,  that  we  make  even  our  gods 
in  our  own  image,  offers  no  warrant  for  supposing  that  nothing  higher 
will  ever  be.  What  ape  could  have  predicted  man,  what  reptile  the 
bird,  what  amoeba  the  bee  ?  ''There  are  many  events  in  the  womb  of 
time  which  will  be  delivered"  and  the  fairest  of  her  sons  and  daughters 
are  yet  to  be. 

But  even  grant,  for  the  sake  of  the  argument,  that  the  intelligence 
of  a  Newton,  the  musical  faculty  of  a  Bach,  the  moral  nature  of  any 
good  mother  anywhere,  represent  the  utmost  limits   of  which  the 


THE  PROMISE  OF  RACE  CULTURE  507 

evolution  of  the  psychical  is  capable.     There  is  every  reason  lo  deny 
this,  but  let  us  for  the  moment  assume  it  true.     There  still  remains 
the  thought  of  Wordsworth,  "What  one  is,  why  may  not  millions 
be?" — a  thought  to  which  Spencer  has  also  given  utterance.     What 
is  shown  possible  for  human  nature  here  and  there,  he  says,  Ls  con- 
ceivable for  human  nature  at  large.    It  is  possible  for  a  human  being, 
whilst  still  remaining  human,  to  be  a  Shakespeare  or  a  St.  Francis; 
these  things  are  thus  demonstrably  within  the  possibilities  of  human 
nature.    It  is  therefore  at  the  least  conceivable  that,  in  the  course  of 
almost  infinite  time  (even  assuming,  say,  that  intelligence  must  ever 
be  limited,  as  even  Newton's  intelligence  was  limited) — some  such 
capacities  as  his  may  be  common  property  amongst  men  of  the 
scientific  type;    and  so  with  other  types.     We  may  answer  Words- 
worth that  there  is  no  bar  thrown  by  Nature  in  the  way  of  such  a  hope. 
Whal  is   possible. — This    of  course   is   speculation    and    of    no 
immediate  value.     I  would  merely  remind  the  reader  that  the  doctrine 
of  optimism,  as  regards  the  future  of  mankind,  which  the  principles  of 
race-culture  assume  and  which  they  desire  to  justify,  was  definitely 
shared  by  the  great  pioneers   to  whom  we  owe  our  understanding 
of  those  principles.     Notwithstanding  grave  nervous  disorder,  such 
as  makes  pessimists  of  most  men,  both  Darwin   and  Spencer  were 
compelled  by  their  study  of  Nature  to  this  rational  optimism  as 
regards  man's  future.     The  doctrine  of  organic  evolution,  and  of  the 
age-long  ascent  of  man  through  the  selection  of  the  fittest  (who  have, 
on  the  whole,  been  the  best)  for  parenthood,  is  one  not  of  despair  but 
of  hope.     Exactly  half  a  century  ago  it  struck  horror  into  the  minds  of 
our  predecessors.     Man,  then,  is  only  an  erected  ape,  they  thought — 
as  if  any  historical  doctrine,  however  true,  could  shorten  the  dizzy 
distance  to  which  man  has  cHmbed  since  he  was  simian;   and  man 
being  an  ape,  they  thought  his  high  dreams  palpably  vain.     But  the 
measure  of  the  accomplished  hints  at  the  measure  of  the  possible,  and 
the  value  of  the  historical  facts  lies  not  in  themselves,  all  facts  as 
such  being  as  dead  as  are  the  individual  atoms  of  the  living  body,  but 
in  the  principles  which  grow  out  of  them.     It  is  of  no  imj^ortance  as 
such  that  man  has  simian  ancestors;  it  is  of  immeasurable  importance 
that  he  should  learn  by  what  processes  he  has  become  human,  and  by 
what,  indeed,  they  became  simian  -which  would  have  been  a  proud 
adjective  for  its  own  day.     The  principles  of  organic  progress  matter 
for  us  because  they  are  the  principles  of  race-culture,  the  only  sure 
means  of  human  progress.     Our  looking  backwards  does  not  turn  us 


5o8      READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 

into  pillars  of  salt,  but  teaches  us  that  the  best  is  yet  to  be,  and  how 
alone  it  is  to  be  attained. 

Elsewhere  the  optimistic  argument  of  Wordsworth  is  quoted. 
Here  also  John  Ruskin: 

"There  is  as  yet  no  ascertained  limit  to  the  nobleness  of  person 
and  mind  which  the  human  creature  may  attain,  by  persevering 
observance  of  the  laws  of  God  respecting  its  birth  and  training." 

And  Herbert  Spencer: 

''What  now  characterizes  the  exceptionally  high  may  be  expected 
eventually  to  characterize  all.  For  that  which  the  best  human  nature 
is  capable  of,  is  within  the  reach  of  human  nature  at  large." 

And  Francis  Galton: 

"There  is  nothing  either  in  the  history  of  domestic  animals  or  in 
that  of  evolution  to  make  us  doubt  that  a  race  of  sane  men  may  be 
formed,  who  shall  be  as  much  superior,  mentally  and  morally,  to  the 
modern  European,  as  the  modern  European  is  to  the  lowest  of  the 
Negro  races. 

"It  is  earnestly  to  be  hoped  that  inquiries  will  be  increasingly 
directed  into  historical  facts,  with  the  view  of  estimating  the  possible 
effects  of  reasonable  political  action  in  the  future,  in  gradually  raising 
the  present  miserably  low  standard  of  the  human  race  to  one  in  which 
the  Utopias  in  the  dreamland  of  philanthropists  may  become  practical 
possibilities." 

Conclusion — eugenics  and  religion. — In  an  early  chapter  it  was 
attempted  to  show  that  eugenics  is  not  merely  moral,  but  is  of  the 
very  heart  of  morality.  We  saw  that  it  involves  taking  no  life,  that, 
rather  it  desires  to  make  philanthrophy  more  philanthropic,  that,  at 
any  rate  so  far  as  this  eugenist  is  concerned,  it  recognizes  and  bows 
to  the  supreme  law  of  love;  and  claims  to  serve  that  law,  and  the 
ideal  of  social  morality,  which  is  the  making  of  human  worth.  Eugen- 
ics may  or  may  not  be  practicable,  it  may  or  may  not  be  based  upon 
natural  truth,  but  it  is  assuredly  moral;  though  I,  for  one,  would  pro- 
claim eternal  war  between  this  real  moraUty  and  the  damnable  sham, 
which  approves  the  unbridled  transmission  of  the  most  hideous 
diseases,  rotting  body  and  soul,  in  the  interests  of  good. 

And  if  religion,  whatever  its  origin  and  the  more  questionable 
chapters  in  its  past,  be  now  "morality  touched  with  emotion," 
I  claim  that  eugenics  is  religious,  is  and  will  ever  be  a  religion.  Else- 
where I  have  attempted  to  show  that  religion  has  survived  and  will 
survive  because  of  its  survival-value — its  services  to  the  Hfe  of  the 


THE  PROMISE  OF  RACE  CULTURE  509 

societies  wherein  it  flourishes.  The  rehgion  of  the  future,  it  was 
sought  to  argue,  will  be  that  which  "best  serves  Nature's  unswerving 
desire — fullness  of  life."  The  Founder  of  liic  Christian  religion  said, 
''I  am  come  that  ye  might  have  life,  and  that  ye  might  have  it  more 
abundantly."  It  is  higher  and  more  abundant  life  that  is  the  eugenic 
ideal.  Progress  I  define  as  the  emergence  and  increasing  dominance 
of  mind.  Of  progress,  thus  conceived,  man  is  the  highest  fruit  hitherto. 
He  is  also  its  appointed  agent  and  eugenics  is  his  instrument. 

To  this  end  he  must  use  all  the  j)owers  which  have  blossomed  in 
him  from  the  dust.  He  must  claim  Art:  and  indeed  in  Wagner's 
great  music-drama,  at  the  moment  when  the  prophetic  Briinnhilde 
tells  Sieglinde  who  has  just  lost  her  mate  that  she,  the  expectant 
mother,  may  look  for  the  resurrection  of  the  dead  and  the  life  of  the 
world  to  come  in  the  child  Siegfried;  and  when  the  heroic  theme  is 
pronounced  for  the  first  time  and  followed  by  that  which  signifies 
redemption  by  love;  then,  I  think,  the  eugenist  may  thrill  not  merely 
to  the  music,  nor  the  humanity  of  the  story,  but  to  the  spiritual  and 
scientific  truth  which  it  symbolizes. 

If  the  struggle  towards  individual  perfection  be  religious,  so, 
assuredly,  is  the  struggle,  less  egoistic  indeed,  towards  racial  perfection. 
If  the  historic  meaning  and  purport  of  rehgion  are  as  I  conceive  them, 
and  if  its  future  evolution  may  thence  be  inferred,  there  can  be  no 
doubt  in  the  prophecy  that  in  ages  to  come  those  high  aspirations  and 
spiritual  visions  which  astronomy  has  dishoused  from  amongst  the 
stars,  and  which,  at  their  best,  were  ever  selfish,  will  find  a  place  on  this 
human  earth  of  ours.  If  we  have  transferred  our  hopes  from  heaven 
to  earth  and  from  ourselves  to  our  children,  they  are  not  less  religious. 
And  they  that  shall  be  of  us  shall  build  up  the  old  waste  places;  for  we 
shall  raise  up  the  foundations  of  many  generations. 

"We  feel  the  high  tradition  of  the  world 
And  leave  our  spirits  on  our  children's  breasts." 


rnOFERTY  UBnART 

Af.  C-  Stiij^  C  -'iff 


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INDEX 


INDEX 


Abiogenesis,  12 
Abraxas,  438,  452 

Acquired  characters,  inheritance  of,  19, 
20,  273;  discussion  by  E.  G.  Conklin, 
33°~3^'>^  lack  of  evidence  for,  332, 
33S;  misunderstandings  concerning, 
323-30;  other  side  of  the  question, 
336-38;  statement  of  the  problem, 
323,  331-32 

Adaptation,  11,  30,  188-205;  classi- 
fication of  adaptations,  195,  196; 
Osborn's  laws  of,  192-95 

Adaptive  radiation,  law  of,  194,  195 
Agassiz,  L.,  144,  145 
Aggressive  resemblance,  201 
Albinos,  different  kinds,  of,  431,  432 
Allelomorphic,  characters  in  heredity, 

433 
Allen,  E.  J.,  209 

Alluring  coloration,  201 

Ameghino,  F.,  86 

Amphioxus,  178 

Amphisbaenidae,  119 

Analogous,  versus  homologous  struc- 
tures, 136 

Anaxagoras,  12 

Anaximander,  11 

Anaximenes,  11,  12 

Ancestral  inheritance,  Galton's  law  of, 

371,  372 
Anti-lens  serum,   Guyer's  experiments 

with,  338-45 
Antirrhinum,  446 
Apartness  of  the  germ  plasm,  31,  295, 

296,  337 
Apotetix,  448 
Appendix    vermiformis,    in    man    and 

apes,  154,  155 
Apteryx  australis,  142,  143 
Aquinas,  Thomas,  8,  15 
Archaesthetism,  35 
Aristotle,  13,  14,  18 
Arithmetical  mean,  367 

Armadillo  quadruplets:  and  classifica- 
tion, 122,  123;  and  sex-determina- 
tion, 45 1 


Armadillos,  97 
Artificial  selection,  25,  26 
Aspergillus  niger,  327 
Atavism,  13 
Atropa,  393 
Augustine,  8,  15 
Azores,  fauna  of,  103 

Babcock,  E.  B.,  287,  307-22,  363,  364, 
401-12 

Bacon,  F.,  15,  276 

Balanoglossus,  177,  178 

Bascanion  anthonyi,  117 

Bat,  wing  of,  134 

Bateson,  W.,  7,  43,  346,  368,  369,  380, 

393,  396,  414,  446 
Bathmism,  35 
Bauer,  E.,  335 

"Beagle,"  Darwin's  voyage  on  the,  23, 

25,  26 

Beebe,  W.,  316,  317 

Beeton,  M.,  485,  489,  491 

Begonia,  337,  338 

Bell,  A.  G.,  474,  491 

Bembidium,  109 

Bequerel,  A.  H.,  275 

Bergson,  H.,  34 

Bermudas,  fauna  of,  103-5 

Bibliography,  510-13 

Billen,  R.  H.,  394 

Bimodal  and  multimodal  curves,  368, 

369 
Biometr}':    discussion  of,  365-75;    rise 
and  vogue  of,  38,  39 

Birds:     rudimentary    teeth    of,     181; 
wing  of,  134 

Birgus  lalro,  138,  139,  140 

Bison  antiquus,  85 

Blakeslee,  A.  F.,  417 

Blastoderm,  166 

Blastula,  166 

Blends,  in  heredity,  416-18 

Blood-transfusion  tests,  evidences  from 

Oo,  124-2S 

Bonnet,  R.,  16 


515 


5i6      READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 


Boyd-Dawkins,  162 

Brachydactylism,  399,  400;  inheritance 

of,  460 
Bridges,  C.  B.,  402,  437 
Briinn,  40,  41 
Bryonia,  436 

Buffon,  G.  L.  L.,  7,  15,  16,  17 
Bullen,  G.  E.,  209 

Cameline:    forefoot,  75;    skull,  evolu- 
tion of,  74 
Camels,  fossil  pedigree  of,  73-76 
Cape  de  Verde  Islands,  fauna  of,  106 
Carnivora,  126 
Carnot,  S.,  277 
Carsinas  maenas,  256 
Castle,  W.  E.,  39,  40,  41,  43,  261,  287, 

333,   334,   378,   379.    399,   43^,   432, 
433-48 

Cataract,  inheritance  of,  461 

Catastrophism,  22,  23 

Cave  animals,  eyes  of,  144,  145 

Cebidae,  126 

Cell:  diagram  of  typical  cell,  291; 
division,  direct,  290,  291;  division, 
indirect  or  mitotic,  291,  292,  403-5; 
division,  somatic,  403-5;  theory,  289 

Cenogenetic,  174 

Centrosome,  290,  291,  292 

Cesnola,  257 

Cetacea,  179 

Chamberlin,  T.  C,  57 

Chambers,  R.,  23,  26 

Chapin,  C.  V.,  483 

Child,  C.  M.,  191,  192,  337 

Child  mortality  in  long-lived  families, 
488 

Chimpanzee,  88 

Chromatin,  290;  interchange  between 
homologous  chromosomes,  408;  nu- 
cleolus, 290 

Chromosomes,  291,  292;  conjugation 
of  pairs  of,  407;  of  Drosophila,  297; 
in  heredity,  304,  305;  independent 
distribution  of,  408,  409;  individual- 
ity of,  296;  maps  to  show  loci  of 
genes,  437,  442;  of  mosquito,  297; 
number  and  appearance,  293;  pairs 
of,  297,  407;  reduction  of,  297-98, 
406;  and  sex  in  Drosophila,  410-12; 
significance  of,  292,  293 

Circopithecidae,  126 


Clark,  J.  M.,  85 

Classification:  basis  of,  11 7-19;  evi- 
dences from,  60,  117-23;  inter- 
national code  of,  117;  method  of, 
120-21 

Clausen,  R.  E.,  287,  307-22,  363,  364, 
401-12 

Cleavage  of  egg,  294 

Cocoanut  crab,  138,  139,  140 

Coefficient  of  correlation,  369,  370 

Coincident  selection,  268,  269 

Color  in  animals,  200-204 

Coluber  anthonyi,  117 

Colubridae,  117 

Colubrinae,  117 

Commensalism,  as  adaptation,  198,  199 

Communal  life,  as  adaptation,  199,  200 

Comparative  Anatomy,  evidences  from, 
60,  129-63 

Confusing  coloration,  204 

Conklin,  E.  G.,  330-37,  370-75.  434,  435 
Conjugation,    of  homologous   chromo- 
somes, 407 

Convergence,  Osborn's  law  of,  192-94 

Cope,  E.  D.,  35 

Correlation:  coefficient  of,  369,  370; 
tables,  370 

Correns,  C,  40,  43,  380,  393,  394,  415, 
416,  424 

Cossonidae,  108 

Coulter,  J.  M.,  386-92,  413-28 

Coulter,  M.  C,  386-92,  413-28 

Coutagne,  G.,  396 

Crampton,  H.  E.,  5,  32,  271 

Cretins  of  Aosta,  464,  465,  478,  479 

Crossing-over,  in  Mendelian  heredity, 
441-48 

Cuenot,  L.,  398 

Curie,  P.,  275 

Cuvier,  G.,  19,  21,  22 

Cytoplasm,  290;  in  inheritance,  304 

Dakin,  W.  J.,  209 

Daphnia,  335 

Darbishire,  A.  D.,  393,  398 

Darwin,  C,  4,  5,  6,  8,  10,  11,  17,  19, 
23,  24,  25,  26,  27,  28,  29,  30,  31,  45,  61, 
67,  97,  118,  120,  121,  160,  205,  210, 
211,  213,  219-44,  259,  260,  307,  330, 

427,477,  501 
Darwin,  E.,  3,  16,  17,  18,  21 


IXDEX 


:)i/ 


Darwmism,_  7,  8;  background  of,  188- 
216;  critique  of,  245-62;  defense  of, 
general,  252-56;  objections  to,  247- 
52 

Dasypus  novemcinctus,  366,  375-78 

Datura,  395 

Davenport,  C.  B.,  257,  333,  372,  393, 
396,  474,  475 

Davenport,  G.  C,  400 

Davis,  B.  M.,  360 

De  CandoUe,  A.,  23,  122 

Defectives,  segregation  of,  479-80 

Democritus,  12 

Dendy,  A.,  71,  73 

Descartes,  R.,  15 

Determinants  (Weismann's),  30,  31,  32, 
265 

Determination  of  sex,  449-56 

Development:  facts  of,  164,  165;  out- 
line of  animal  development,  165-72 

De  Vries,  H.,  7,  36,  37,  38,  39,  43,  258, 
260,  261,  273,  335,  346-60,  380,  393, 
429 

Difficulties  and  objections  to  Natural 
Selection  as  seen  by  Darwin,  236-42. 

Difflugia,  378 
Digby,  L.,  363,  364 
Dihybrid  ratio,  391 
Dinornis  gravis,  136,  137,  142 
Dominance,  Mendel's  Law  of,  40-42, 
381,  382,  386 

Doncaster,  L.,  399 

Downing,  E.  R.,  459-72 

Driesch,  H.,  34 

Drinkwater,  H.,  400,  460 

Drosophila  ampelophila,  318,  321,  380, 

444;   chromosomes  of,  401,  402,  403; 

sex-linked  heredity  in,  433~38 
Drummond,  H.,  214,  215 
Durham,  F.  M.,  429,  430 

Ears  of  man  and  apes,  155,  156,  157 

Earthworms  and  vegetable  mold,  214 

East,  E.  M.,  43,  419 

Eaton,  Rev.  A.  E.,  143 

Ectoblast,  166 

Edentates,  distribution  of,  98 

Edwards,  J.,  483 

Eimer,  T.,  34,  35,  264 

Elderton,  E.  M.,  493 

Electric  organ,  of  fishes,  196 


IMcphants,  evolution  of,  76-80 

l-^lephas,  76,  77,  78,  79,  80;  K.  autiquus, 
.Sg;    E.  columhi,  85;    E.  leidyi,  H5 

Embryology,  evidences  from  ^o,  164-72 

Ivmpedocles,  12,  13 

Endoblast,  166 

Kngrammcs  of  Rignano,  335 

Enteleche,  34 

Environment:  cfTects  of,  on  develop- 
ment, 317,  3i8;etTc(ts  of,  on  hi-redity, 
312-16,  318-20;    and  heredity,   312, 

in 

EoanthropHS  dawsoni,  93 

Epicurus,  14 

Epigenesis,  13 

Epilepsy,  inheritance  of,  465 

Equidae,  70,  71,  72,  73 
Equus,  71,  72,  73;  E.  leidyi,  85 
P^scherich,  215 

Eugenics:  Carnegie  Laboraton.'  of,  459; 
and  cruelty  to  children.  502,  503; 
defined,  473;  Education  Society,  505; 
and  Euthenics,  484-96;  Galton 
Laboratory  of,  459;  positive,  480-83; 
and  religion,  508,  509;  restrictive, 
475-480;  and  unemployment,  501, 
502;  and  woman,  502 

Eupagurus,  246 

Euthenics,  473,  484-96 

Evolution,  organic:  causal  factors  of, 
185;  definitions  of,  3,  4,  5 1  evidences 
of,  59,  60;  experimental.  60;  nature 
of  proof  of,  59;  proof  of,  57,  58,  59; 
what  it  is  not,  8,  9 

Fabre,  M.,  231 

Factor  hypothesis,  417*28 

Factorial  analysis  of  color  in  mice,  429- 

30 
Factors,    in    Xeo-Mendelian    heredity: 

complementary,  417-20;  cumulalive. 

424;    inhibitory.  421-23;    lethal,  432; 

in  quantitative  inheritance,  424-28 

Farmer.  J.  H..  363,  364 
Farrabee,  \V.  C\,  400 
Feeble-mindedness,  inheritance  oi,  403, 

464 
Fertilization,  301,  302 
Fierasfcr  acus,  198,  lOO 
Filiiria  sanguinis  hominis,  212 
Filial    Regression,    Gallon's    Uiw    of, 

372-74 
Flower,  Professor,  1O2 


5l8      READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 


Forfictilata  auricularia,  368,  369 

Franklin,  B.,  482 

Freemartin,  455,  456 

Fossils:  actual  remains,  63 ;  Cambrian, 
62;  casts  and  impressions,  64;  classi- 
fication of,  63;  conditions  necessary 
for,  64,  65,  66;  Dar.win's  opinion  as 
to  the  adequacy  of  the  record,  of  the, 
61,  62;  definition  of  (by  T.  H. 
Huxley),  63;  first  recognized,  12; 
general  facts  revealed  by,  69,  70; 
pedigrees  of  well-known  vertebrates, 
70-80;  petrifications,  63 

Gadow,  H.,  114,  115 

Gager,  C.  S.,  361 

Galapagos  Islands,  fauna  of,  105-7 

Gallastegui,  448 

Galton  Laboratory   of  Eugenics,  459, 

474 
Galton,  Sir  F.,  38,  39,  365,  370-75,  376, 

473,  497-501,  505,  508 
Gastrula,  166 
Gates,  R.  R.,  363 
Gazelle-camels,  76 
Gegenbaur,  175 
Gemmules,  28,  30 

Genealogical  Records  Ofiice,  484,  491, 
492 

Genetics:  definitions  of,  287;  evi- 
dences from,  60;  importance  of  cell 
theory  in,  289;  methods  of  study, 
288;  scope  and  methods  of,  287-89; 
subject-matter  of,  288-89 

Genius:  hereditary,  498;  production  of 
497,  498;    transmission  of,  498,  499 

Genotype,  377-79 
Genotypic,  377-79 

Geographic  distribution,  evidences 
from,  60,  97-116 

Geologic  time:  lapse  of,  67,  68;  scale 
in  millions  of  years,  68 

Germ-cells:  early  setting  apart  of,  295, 
296;  origin  of  new,  294,  295;  pro- 
duction of,  405-8 

Germinal  continuity,  31,  296 

Germinal  selection,  30,  31,  265-68 

Germ-plasm  theory,  31,  32  - 

Giekie,  Sir  A.,  69 

Gill  arches  in  vertebrates,  176,  177 

Giraffe-camels,  76 

Glaser,  O.  C,  365 

Glochidia,  211 


Goddard,  H.  H.,  462-64 

Goethe,  J.  W.,  21 

Goldschmidt,  R.,  314,  315,  453 

Goodale,  H.  D.,  440 

Gorilla,  149 

Goss,  J.,  40 

Graham-Smith,  G.  L.,  125 

Gray,  A.,  223 

Greek  evolutionists,  11-14 

Gregory  of  Nyssa,  14 

Gregory,  R.  P.,  445 

Gregory,  W.  K.,  82 

Guacanos,  73 

Gulick,  J.  T.,  32,  271 

Guthrie,  C.  C,  S33 

Guyer,  M.  F.,  289,  290-306,  336,  338-45 

Habitat:  preference,  190,  191;  selec- 
tion, 190,  191 

Haeckel,  E.,  19,  30,  172,  173 

Hair  of  man  and  apes,  156-61 

Haldane,  443,  444 

Hamilton,  D.  J.,  326 

Hapalidae,  126 

Harris,  J.  A.,  335,  485 

Harrison,  R.  G.,  333 

Harte,  Bret,  85 

Hartmann,  C.  G.,  162 

Harvey,  W.,  13 

Hauser  blonds,  481 

Hegner,  R.  W.,  295 

Helix  hortensls,  396;  H.  nenioralis,  396 

Henderson,  L.  J.,  189 

Heraclitus,  12,  208 

Herbert,  S.,  263,  264,  269 

Heredity:  Galton's  Laws  of,  371-75; 
in  man,  398-400;  in  pure  lines,  376, 
379;  statistical  study  of,  370-75 

Hermit-crabs,  138 

Heron,  Sir  R.,  231 

Herschel,  Sir  J.,  3 

Heterogenesis  theory,  36 

Heteromera,  106 

Heterozygote,  390 

Hialodaphnia,  315,  316 

Hippocrates,  449 

Homo:  H.  heidelhergensis,  88;  H.  sa- 
piens, 88,  90,  92,  93;  H.  neander- 
thalensis,  89,  90,  91,  92,  93;  H. 
primagenius,  89 


INDEX 


519 


Homologies,  evidences  from,  60 
Homozygote,  390 
Hooker,  Sir  J.,  109,  223,  247,  330 
Hormone  theory  of  sex  differentiation, 

454-56 
Hormones,  454 

Horse:  ancestr>'  of,  8;  feet  and  teeth  in 
fossil  pedigree  of,  72;  fossil  pedigree 
of,  70,  71,  72,  73 

Horseshoe-crab,  127 

Hrdlicka,  A.,  86 

Hudson,  W.  H.,  206 

Human  antiquity,  evidences  of,  93,  94 

Human  conservation,  473-83 

Humanity,  future  of,  95,  96 

Humerus,  perforations  of,  in  Quadru- 
mana,  162 

Hurst,  C.  C,  43>  393,  396,  399,  400 

Hutton,  J.,  22,  57 

Huxley,  T.  H.,  28,  29,  62,  63,  91,  208 

Hyatt,  A.,  35 

Hybridization  and  the  origin  of  species, 

43 
Hyracotherium,  71 

Immigration  and  eugenics,  475-76 

Immunity  coloration,  203 

Induction,    a    temporary    change    in 

germ-cells,  335,  336 
Infant  mortality  movement,  494 

Inheritance:  of  acquired  characters 
{see  Acquired  characters);  of  brachy- 
dactylism,  460;  of  cataract,  461; 
of  feeble-mindedness,  459,  462-64; 
of  human  characters,  459-72;  of 
insanity,  epilepsy,  etc.,  459,  465,  466; 
in  royalty,  466-72;  sex-linked,  433~4o 

Insanity,  inheritance  of,  465 

Intraselection,  268 

Isolation:     biologic,    272;     geographic, 

269-72;   theories  of,  20,  32,  2;^,  269- 

73;   reproductive,  272,  273 

Jennings,  H.  S.,  261,  377,  378 
Johannsen,  W.,  369,  376,  377 
Johnson,  R.  H.,  484-96 
Jones,  D.  F.,  448 

Jordan,  D.  S.,4,  32,  33,  34,  63,  64,  65, 66, 
121,  165-74,  188,  195,  202,  270,  271, 
273,  478,  479,  482 

Joule,  J.  P.,  277 

Judd,  J.  W.,  10,  23,  24 


Kallima,  201,  204,  250 
Kammerer,  P.,  336 
Kant,  E.,  15,  16 

Kellogg,  V.  S.,  4,  32,  33,  34,  63,  64,  65, 
66,  121,  165-74,  188,  195,  202,  245- 
47,  253,  266,  273 

Kelvin,  Lord,  67,  68,  277 

Kinetogenesis,  35 

King,  C,  67 

Klebs,  E.,  312,  313 

Knight,  T.,  40 

Kohlreuter,  J.  C,  40,  41 

Korchinsky,  H.,  36 

Lamarck,  J.  P.,  7,  10,  11,  18,  19,  20,  21, 

118,  247,  307,  330,  345 
Lamarckism,  7,  21,  247 
Lang,  A.,  395 
Laplace,  P.  S.,  57 
Laplacian  hypothesis,  67 
Laughlin,  H.  H.,  474 
Le  Conte,  J.,  3,  46-53 
Leibnitz,  15 
Leighty,  C.  E.,  370 
Lemuroidea,  126 
Lepas,  metamorphosis  of,  171 
Lepidosiren,  236 

Lcptinotarsa  deccmliniala,  321,  361,  377 
Lillie,  F.  R.,  455,  456 
Liua  lapponica,  396 
Lincoln,  A.,  24 

Linkage,  in  Mendelian  heredity,  441- 
48;  chromosome  thcor>'  of,  442; 
measurements  of,  444,  445 

Linnaeus,  16,  43,  117 

Locy,  W.  A.,  41,  42,  43 

Loeb,  C,  461 

Loess  Man,  85 

Lotsy,  J.  P.,  43 

Love,  H.  H.,  370 

Lowell,  J.  R.,  330 

Lucas,  A.  H.  S.,  218 

Lucretius,  14 

Lull,  R.  S.,  3,  5,  24,  25,  73.  76,  79,  Si-96 

Lychnis,  393,  436 

Lydekkcr,  R.,  178 

Lyell,  Sir  C,  3,  8,  '-3,  26,  57,  5^.  67 

Maas,  O.,  180 

Macdougal,  D.  T.,  319,  320,  361,  362 

McCracken,  I.,  396 


520     READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 


McFarland,  J,,  28 

McGregor,  J.  H.,  90 

Madagascar,  fauna  of,  no,  in 

Maeterlinck,  200 

Mallophaga,  271,  272 

Malthus,  17,  23,  24,  26,  223 

Mammalian  dispersal,  1 14-15 

Mammary  glands,  as  adaptations,  196 

Man:  of  Chappelle-aux-Saints,  91; 
Cro-Magnon  Man,  93,  94;  chrono- 
logical table  of  fossil  man,  87 ;  descent 
from  trees,  significance  of,  84;  evolu- 
tion of,  81-96;  evolutionary  changes 
of,  84;  fossil  man,  84-94;  Heidel- 
berg Man,  88,  89,  91;  impelling 
cause  of  origin,  83;  Neanderthal 
Man,  89-92;  origin  of,  82-84;  Pilt- 
down  Man,  92,  93;  place  of  origin, 
82,  83;  of  Spy,  91;  stock  of,  82; 
time  of  origin,  83,  84 

Mantis  religiosa,  257 

Marriage  laws  and  eugenics,  477 

Marsh,  O.  C,  72 

Marshall,  A.  M.,  214 

Marsupial  pouch,  as  adaptation,  196, 
197 

Mastodon,  76,  77,  78,  79,  85 
Materialism,  the  relation  of  evolution 

to,  46-53 
Matthew,  W.  T.,  81 
Matthiola,  394 

Maturation:  of  egg-cell,  299,  300,  301; 
of  sperm-cell,  298,  300 

Maupertius,  15 

Median,  in  variation,  367 

Meek,  364 

Megalonyx  jefersoni,  85 

Mendel,  G.,  40,  260,  346;  his  concep- 
tion of  purity  of  gametes,  386,  387; 
his  conception  of  unit  characters,  386; 
his  experiments,  381;  his  explana- 
tions, 386-92;  his  Law  of  Domi- 
nance, 40-42,  381,  382,  386;  his  Law 
of  Segregation,  4C^42,  382-385; 
his  life  and  character,  380;  his  results, 
381,382 

Mendelian  heredity:  in  cats,  399; 
crossing-over  in,  441-48;  in  guinea- 
pigs,  399>  432,  433;  in  Helix,  396; 
in  Lina  lapponica,  396;  linkage  in, 
441-48;  in  maize,  394,  394;  in  man, 
399,  400;  in  mice,  384,  385,  398; 
in  nettles,  395;  in  numerous  species, 
393>  394;    in  peas,  384;    in  pigeons. 


397,. 398;    in  poultry,  396,  397;    in 
rabbits,  399;  in  silkworms,  395,  396 

Mendelism:   physical  basis  of,  401-12 

Mesohippus,  72 

Metcalf,  M.  M.,  6,  32,  200-204 

Metz,  C.  E.  v.,  297,  363,  436 

Meyer,  L.,  155 

Miastor  americana,  294,  295 

Millson,  A.,  214 

Milton,  J.,  14 

Mimicry,  203 

Miohippus,  72 

Mirabilis  jalapa,  394,  415,  416,  424; 
M.  rosea,  394 

Mivart,  135,  136 

Mneme  theory  of  Semon,  335 

Mode,  in  variation,  367 

Modifications,  308,  309 

Moeritherium,  76,  77,  78 

Monohybrid  ratio,  389 

Moore,  C.  R.,  454 

Morgan,  L.,  264 

Morgan,  T.  H.,  42,  43,  44,  260,  261,  267, 

318,  321,  355-60,  379,  433-38,  442, 

443 
Morphology,  evidences  from,  129-63 
Moulton,  F.  R.,  57 
Miiller,  P.,  170,  172,  239 
Miiller,  H.  J.,  408,  437 
Multiple  factor  hypothesis,  424-28 

Mutation  theory,  346-64;  advantages 
over  Natural  Selection,  359;  alterna- 
tive to  Natural  Selection,  272;  criti- 
cism of,  359-60;  De  Vries'  own 
account  of,  348-55;  historical 
account  of,  36-38;  Morgan's  sum- 
mary of,  355-59 

Mysis  larva  of  Peneus,  170 

Nabours,  R.  K.,  448 
Nageli,  C.  von,  34,  35,  7,2>2>,  380 
Natural  Selection,  4,  12,  24,  25,  26,  35, 
37,  38,  223-43;  experimental  sup- 
port of,  256-58;  present  status  of, 
258;  relation  of  Mendelism  and 
mutation  to,  258-62 

Naudin,  C,  41 

Nauplius  larva  of  Peneus,  170 
Neanderthal  Man,  88-92 
Nebular  hypothesis,  57 
Neo-Lamarckism,  29,  335,  336 


INDEX 


521 


Neo-Mendelism,  43,  44,  45,  413-32 

Nest-making  instincts,  as  adaptations, 
197 

Nettleship,  E.,  400,  461 

Newman,  Colonel,  211 

Newton,  Sir  F.,  7,  276,  277,  280,  283 

New  Zealand,  fauna  of,  no,  in 

Nictitating  membranes  of  vertebrates, 
146,  147 

Nilsson-Ehle,  H.,  424-28 

Nitsche,  Dr.,  155 

Nucleolus:   chromatin,  290;   true,  290 

Nutritive  chains,  208 

Nuttall,  G.  H.  F.,  124,  125 

Nutting,  C.  C,  258-62 

Oceanic  islands,  fauna  of,  loi-io 

Octopus,  eye  of,  135 

Oenothera,  35;  O.  albida,  _iS5>  ^^ 
biennis,  349;  0.  brevistylis,  349  ff- 
O.  elliptica,  355;  0.  gigas,  353  ff. 
O.  lata,  355;  O.  laevifolia,  349  ff. 
O.  lamarckiatta,  37,  346-60;  0 
leptocarpa,  357;  0.  nannella,  349  ff. 
O.  rubrinervis,  353  flf.;  0.  sciniillans, 
355;   0.  spattdata,  357 

Oglivie,  Dr.,  326 

Oken,  12,  16 

Onagra  biennis,  362 

Ontogenetic  selection,  268 

Oocyte,  300 

Oogenesis,  299,  300 

Oogonium,  300 

Organic  selection,  268,  269 

Origin  of  Species,  The,  4,  5,  7,  24,  27, 

61,  62,  67 
Ornithorhynchus,  236 
Orohippus,  72,  73 
Orr,  H.  B.,  465 

Orthogenesis,  33,  34,  35,  3^,  273 
Orthoplasy,  268 
Osborn,  H.  F.,  8,  10,  11,  13,  20,  21,  45, 

86,  87,  89,  94,  95,  192-95,  273,  274-83 
Overspecializations,  31 
Ovum,  164 
Owen,  R.,  121,  150,  240 

Pagurus  bernhardus,  139 

Palaeomastodon,  76,  77,  78 

Palaeontology,  evidences  from,  60; 
opinions  as  to  the  adequacy  of,  62,  63; 
strength  and  weakness  of,  6r,  62 


ralingenctic,  174 

Pan  vctus,  88 

Pangenesis,  28,  30 

Panmixia,  31,  263,  264 

Panniculus  carnosis,  148,  149 

Papilio  machaon,  315 

Paramecium,  377 

Parasitism,  as  adaptation,  197,  198 

Parthenogenesis:  as  a  method  of 
asexual  de\cl()|)ment,  164;  sex  deter- 
mination in  connection  with,  451,  452 

Pearl,  R.,  440 

Pearson,  K.,  39,  365,  371,  373,  484,  489, 

491,  493 

Pedigree:  of  brachydactylism,  460; 
of  cataract,  461;  of  Charles  the 
Great  of  Sweden,  471;  of  feeble- 
mindedness, 463,  464;  of  Ferdinand 
and  Isabella,  468;  of  HohenzoUcms 
of  Prussia,  470;  of  insanity,  epilepsy, 
etc.,  465;  of  Romanoffs  of  Russia, 
467 

Peneus  potitniriiim,  170,  171 

Phaseolus,  376 

Phenotype,  377-79,  39°,  43 1 

Phenotypic,  377-79,  39°,  43 1 

Phillips,  J.  C,  m 

Phocochaerus,  324,  325 

Physiological  units,  28 

Pisum  qiiadraium,  381 ;  P.  saccharalum, 
381;  P.  sativum,  iqy,  P.  umbdlatum, 
381 

Pithecanthropus  ercctus,  86,  87,  88,  90,  93 

Planetesimal  hypothesis,  57 

Plate,  L.,  264,  265,  371 

PUny,  14 

Pliohippus,  72 

Ploetz,  A.,  489,  490,  491 

Podocor>'ne,  246 

Poebrotherium,  74,  75 

Polar  bodies,  299,  300,  301 

Popenoe,  P.,  484--96 

Post-Aristotelians,  14 

Poulton,  E.  B.,  257 

Preformation  doctrine,  176 

Prenatal  influences,  13,  14 

Presence  and  absence  hypothesis.  413- 

15 
Primates:  geologic  record  of,  82;  origin 
of,  81,  82;   place  of  origin;   slock  of, 
81;  time  of  origin,  81 


52  2      READINGS  IN  EVOLUTION,  GENETICS,  AND  EUGENICS 


Primula  kiwensis,  364;  P,  sinensis,  317, 

394,  445 
Priority,  law  of,  117 
Probable  error,  368 
Procamelus,  74,  75 
Promise  of  Race  Culture,  497-509 
Pronucleus:  male,  301;  female,  302 
Protective  resemblance,  200,  201 
Protohippus,  72 
Protylopus,  74,  75 
Pterodactyl,  wing  of,  134 
Punnett,  R.  C,  385,  395,  396,  446 
Pure  lines,  heredity  in,  376-79 
Purity  of  gametes,  386,  387 
Python,  hind  limbs  of,  141,  142 

Quadrumana,  148 

Rabl,  C,  166 

Race  culture  and  human  variety,  504, 

505 
Rana  sylvatica,  333;  R.  palustris,  333 

Recapitulation,   doctrine   of,    60,    171, 
172;   critique  of,  173-82 

Reduction  divisions,  in  maturation,  405 

Reighard,  J.,  203 

Remora,  199 

Reversion,  13 

Revival  of  Science,  the,  15,  16 

Rhodeus  amarus,  212 

Rignano,  E.,  335 

Robinson,  L.,  151,  152 

Rodentia,  loss  of  teeth  in,  180 

Romanes,  G.  J.,  35,  loi-io,  129-63,  263, 
264,  329 

Roosevelt,  T.,  217 

Rosanoff,  A.  J.,  465 

Roux,  W.,  268 

Rumford,  B.  T.,  277 

Ruminants,  collar-bone  of,  180 

Ruskin,  J.,  503,  504,  508 

Ruskin  and  race  culture,  503,  504 

Rutherford,  E.,  275 

Sacculina,  171,  181,  198,  453 
Saleeby,  C.  W.,  497-509 
Saltatory,  variations,  38 
Sandwich  Islands,  fauna  of,  109,  no 
Saunders,  393 


Scardafella  inca,  316,  317;  S.  dialeucos, 
316,  317;  5.  braziliensis,  316,  317; 
S.  ridgwayi,  316,  317 

Schoetensack,  Dr.,  89 

Schuchert,  C,  67,  68,  69 

Scott,  W.  B.,  5,  6,  62,  63,  73-6,  82,  123- 
28, 173-82 

Scrophularia,  319,  320 

Seals,  comparative  anatomy  of,  129,  130 

Secondary  sexual  characters,  453,  454 

Sediim  spectahile,  312-14 

Segregation,  Mendel's  Law  of,  40-42, 
382-85 

Semon,  R.,  335 

Serology,  evidences  from,  60 

Sex  determination,  449-56;  chromo- 
some mechanism  of,  in  Drosophila, 
410  ff.;  in  parthenogenetic  species, 
451,  452;  nutrition  theory  of,  449; 
at  time  of  fertilization,  449,  450; 
various  theories  of,  449-51 

Sex  differentiation,  453-56 

Sex,  Heredity  and,  44,  305,  306 

Sex-linked  inheritance,  433,  440 

Sexual  coloration,  204 

Sexual  Selection,  26,  230-32 

Shelford,  V.  E.,  190 

ShuU,  A.  F.,  73,  76-80,  100,  loi,  117-20 

Shull,  G.  H.,  43 

Signals  and  recognition  marks,  203,  204 

Sims,  G.  R.,  503 

Smith,  E.  A.,  339 

Smith,  G.,  453 

Snow,  E.  C,  493 

Solidago  virguarea,  324 

Species,  definitions  of,  121,  122 

Spencer,  H.,  4,  19,  28,  29,  264,  325,  508 

Spermatid,  298,  299 

Spermatocyte,  298,  299 

Spermatogenesis,  298,  299 

Spermatogonium,  298,  299 

Spermatozoon,  165,  298,  299 

Spontaneous  generation,  12 

Sports,  38 

Sprengel,  C.  K.,  210 

Standard  deviation,  367,  368 

Staples-Brown,  R.,  397 

Statistical  study:  of  variation,  365-70; 
of  heredity,  370-75 

Stegodon,  76,  77,  78,  79 


INDEX 


523 


Steinach,  E.,  454 

Steinmann,  G.,  6 

Stejneger,  117 

Sterilization  laws,  479,  480 

Stock  on  graft,  no  influence  of,  m,  334 

Stockard,  C.  R.,  322,  335 

St.  Helena,  fauna  of,  107-9 

St.  Hilaire,  E.  G.,  21,  22,  220 

Strangevvays,  T.  S.  P.,  125 

Sturtevant,  A.  H.,  437 

Subsidizing  the  fit,  480-82 

Survival  of  the  Fittest,  223-30 

Swainson,  122 

Synapsis,  298,  407 

Systema  Naturae,  of  Linnaeus,  117 

Tail,  vestigial  in  man,  152,  153 

Talent,  the  production  of,  499,  500 

Tasmanian  Wolf,  127 

Tayler,  J.  L.,  253-56 

Taxonomy,  the  method  of,  119-20 

Teleology,  13 

Termites,  214,  215 

Tetrakinetic  theory  of  Osborn,  274,  275- 

83 
Thales,  11 

Theologians,  the  early  Christian,  14,  15 

Thompson,  A.,  153 

Thomson,  J.  A.,  97,  191,  205-18,  323- 
30,  380-85,  393-400 

Tibia,  flattening  of,  in  man,  162 

Tomes,  C.  S.,  161 

Tower,  W.  L.,  321,  322,  360,  361,  377 

Toyama,  K.,  393,  395 

Trihybrid  ratio,  391,  392 

Trilophodon,  76,  77,  78,  79 

Tschermak,  40,  43,  380,  393 

Turner,  Sir  W.,  161 

Tuttle,  E.,  483 

Twins,  evidences  from  in  support  of 
classification,  122 

Typhlopidae,  119 

Uhrschleim,  12,  16 
Uniformitarianism,  22,  23 
Unit  characters,  Mendelian,  386 
Urtica  dodarti,  394,  395;    U.  pilulifcra, 
394,  395 


Vam-ssa  io,  314,  3^5 

Variation,  307-22;  classification  of, 
308-11;  concept  of,  308;  continuous 
and  discontinuous,  311,  346;  and 
development,  311;  and  environment, 
312;  germinal,  308;  nature  of,  309, 
310;  polygons  of,  366,  367;  somatic, 
308;  statistical  study  of,  365-70; 
universality  of,  307,  308 

Vasectomy,  479 

Vestigial    structures,    evidences    from 

60,  140-63 

Virchow,  R.,  91,  240 
Volta  Bureau,  474 

Wagner,  M.,  269,  270 

Walcott,  C.  W.,  62,  64,  67 

Wallace,  A.  R.,  17,  26,  27,  36,  97-100, 
110-13,  122,  239 

Walter,  H.  E.,  373,  473-83 
Warning  coloration,  202,  203 
Weismann,  A.,  3,  7,  30,  31,  32,  195,  247, 

258,  260,  263-68,  281,  330-31,  428 
Weismannism,  7 
Weldon,  W.  F.  R.,  256,  257 

Whales,  comparative  anatomy  of,  131- 
Ss;  embryology  of,  179,  iSo 

White,  G.,  206,  212,  213 

White,  T.  H.,  320 

Whitman,  C.  O.,  35 

Whitney,  D.  D.,  335 

Whymper,  479 

Wilberforce,  Bishop,  28,  29 

Williston,  S.  W.,  35,  83,  85 

Wilson,  E.  B.,  6,  44,  401 

Wings,  comparative  anatomy  of,  134 

Woltereck,  R.,  315,  316,  335 

Woods,  F.  A.,  466-72 

Woodward,  88,  92 

Woolner,  155 

Wordsworth,  W.,  507 

Wright,  Sewall,  164,  165 

Wyman,  Professor,  150 

Xenophanes,  12 

Zca  mays,  395 

Zicgler,  E.,  326 

Zoea  larva  of  Pcneus,  1 70 

Zygote,  165,  297 


